This is my strategy guide on how to beat Shock Defence with 100% HP (and a cool symmetrical layout along with it).

By strategy guide, I mean screen shots of each level. The screen shots are actually taken one level behind, in the preparation phase before moving on to the next level. It took me a few tries, so the money and points might not be fully accurate between some screen shots, though for the last few screen shots, I made it 100% of the way through with 100% HP, so it's possible. I made sure with each playthrough, I did the exact same thing in each of the screen shots, save for the one that didn't work, which I then edited to match the layout that did work.

This layout did get me 100%, though it's not as efficient as my first series of screen shots, which I lost over a year ago. This one still works, though this time I didn't get to upgrade any of my lightning towers to level 4.

Also, results may vary, seeing how enemy lineup formations and rhythm of tower fire may not be the same for each playthrough. If you notice I seem to have more money than you in some of the screen shots, it's because I tend to sell my unneeded towers during a level before all the enemies are wiped out, because as soon as they are, you get a money % bonus depending on how much you have when the last enemy was killed. For example, if you have $100 and you get a 10% bonus, you'll get an extra $10, but if you sell a tower for $75 before the last enemy dies, that's an extra $7 at the end.

This method tries to conserve as much money as possible for the % bonus, to be able to purchase more at the end, which is why a lot of levels have the same layout, and why the Money upgrade is the first purchased, increasing the 10% bonus to 15%.

Anyway, without further rambling, the layouts:

Level 1: Start off with two cannons at base level. Make sure they're in exact position. It matters.

Level 2: Add another cannon at the bottom. Again, precise placing is important. Upgrade the top cannon to level 2.

Level 3: Simply upgrade the bottom cannons to level 2 and watch the show.

Level 4: Upgrade the top cannon. You won't need more firepower than this

Level 5: Leave it the same as level 4. You really don't need more firepower yet.

Level 6: These suckers are fast. Upgrade all existing cannons to level 3 and add another to where it's shown in the pic. You have an 80-90% chance at clearing it perfectly with just the three, and a 110% chance with the extra level 1 cannon, which you will need later anyway.

Level 7: Pretty much every level until the Martian Ships is easier than level 6, so keep the layout as was for level 6. Save your money.

Level 8: Again, make no changes yet. Select the money upgrade.

Level 9: Stay the course. Still no changes needed yet.

Level 10: Still not yet. Keep resting easy.

Level 11: Now add air-only cannons in precisely the location where they are, leaning a bit inward for maximum coverage. Upgrade them to level 3, but keep the bottom cannon at level 1 still.

Level 12: Sell the air-only cannons for money, since they're not need, though you will need them again soon, so you might not have to sell them. Selling them works though, so go with that if you're not sure. Add extra cannons where shown, with an air/land cannon in dead center, and upgrade all to level 3.

Level 13: Keep everything as was for level 12.

Level 14: Again keep everything as is. Try selling the bottom air-only cannon before the last enemy dies.

Level 15: Upgrade to the Lightning Tower. If you haven't already sold the bottom air-only cannon, sell it and replace it with the lightning tower at level 1.

Level 16: Place another level 1 lightning tower above the top middle cannon. Leave everything else as is.

Level 17: Purchase another lightning tower and place it below the bottom one where shown. The bottom one, which is now the middle one, gets upgraded to level 2.

Level 18: Leave everything as is, but upgrade the top lightning tower to level 2. Sell the rightmost air-only cannon before the last enemy falls if possible. If memory serves, you might also be able to sell the last remaining air-only cannon.

Level 19: If you hadn't already sold the rightmost air-only cannon in the last level, sell it now, and possibly even the other air-only cannon. Upgrade the bottom lightning tower so all are at level 2.

Level 20: Sell any remaining air-only cannons. That's pretty much it. If you've already sold them both between level 18 and 19, then you don't have to do shit.... except for upgrading the middle lightning tower to level 3.

Level 21: Upgrade the top lightning tower so everything's at level 3 save for the bottom lightning tower. Sell the top-rightmost cannon before the last enemy falls, if possible.

Level 22: Acquire the Fire Tower upgrade. Sell the top-rightmost cannon if you already haven't. Upgrade the bottom lightning tower to level 3. Purchase the fire tower and place it near the last cannon you just sold, more to the right while facing towards the center more for maximum coverage. Keep it at level 1. Sell the topmost ramaining cannon before the last enemy falls if possible.

Level 23: Sell the topmost remaining cannon if you already haven't. Buy another fire tower and place it where shown, forming sort of a diagonal line with the other fire tower moving towards the center.

Level 24: Keep everything as was for level 23. Easy peasy. Sell the leftmost remaining cannon before the last enemy falls if possible.

Level 25: Sell the leftmost remaining cannon if not already sold. Replace it with another fire tower and upgrade it to level 2. Upgrade the leftmost level 1 fire tower to level 2 as well, leaving the rightmost one at level 1. Sell all remaining cannons before the last enemy falls if possible.

Level 26: Sell all remaining cannons if not sold already. Upgrade the fire towers so that the middle one is at level 3 and the remaining two are at level 2.

Level 27: Upgrade the leftmost fire tower to level 3 so that only the rightmost tower is at level 2.

Level 28: Upgrade the rightmost fire tower so that all present towers are at level 3.

Level 29: Acquire the last remaining tower upgrade, the Poison Tower, and purchase. Place it where shown without upgrading it. Upgrade the middlemost fire tower to level 4.

Level 30: Upgrade the poison tower to level 4 now. Purchase the Super Tower and place it in the dead center where shown. No need to upgrade it yet.

Level 31: Same layout as level 30. Leave everything as is.

Level 32: Now upgrade your super tower to level 2 and proceed to obliterate.

Level 33: You were overpowered in level 32, so keep everything as is.

Level 34: Now things get harder. Buy two more super towers and place them where shown, in a triangle. Upgrade either one to level 2, while keeping the other at level 1. I prefer the leftmost, but I doubt it matters much.

Level 35: Upgrade the last super tower. Purchase two more poison towers and place them in the top-left and bottom-right corners, facing a bit towards the center, and upgrade them fully. You may or may not be able to buy the last $25 upgrade for one of the poison towers. As you see, I just made it.