put your guns on the outer edges of the building area, and have nothing in the middle. Enemies will shoot at the empty center, making bullets pass through your tank harmlessly.
This would be my favorite game on here, if it actually worked for me. but why would they downgrade the ads? It's like the song C.R.E.A.M. except with a T. for "them".
 "Warlords: Call to Arms"){kind=icon}
 "Swarm Simulator"){kind=icon}
 "Soviet Rocket Giraffe Go Go Go!"){kind=icon}
 "Alien Anarchy"){kind=icon}
 "Battalion Commander"){kind=icon}
 "Bloons TD 5"){kind=icon}
 "WarLight"){kind=icon}
 "Pandemic 2"){kind=icon}
 "Bubble Tanks Arenas"){kind=icon}
 "Dolphin Olympics 2"){kind=icon}
 "CellCraft"){kind=icon}
 "Crush the Castle Players Pack"){kind=icon}
 "Loved"){kind=icon}
 "Bubble Tanks Tower Defense"){kind=icon}
 "The Company of Myself"){kind=icon}
 "The Heist"){kind=icon}
 "Frontier"){kind=icon}
 "Blocks With Letters On"){kind=icon}