Cheats > Game > Cheat: 46661

Invincibility
27937

Click on the word "PATROL" at the title screen in the order R, L, A, O, T, and P to enable cheat mode. Click on the "Invincibility" button, then type brokenbombs. Bombs will now have no effect on the buildings. Note: This cannot be used simultaneously with the "Unlimited ammunition" code.