i need help for a level im making...

many people know that gun9 can be used to shoot through walls (as well as bouncers). is there any way to stop that? i tried using riochet but that didnt work. i know you can use trigger crates or gun barrels to stop the gun9, but:

trigger crates can be destroyed by TNT and cannot be regenerated;

gun barrels can be easily regenerated but shoot out ammo when destroyed (by tnt is what i mean) and doesnt look too good.

does anyone know any other way to stop this? i know you can make the barrels/crates go somewhere else in the middle of higher tiles so that tnt will not be affected, but i already made that spot and i dont want to erase it. the tileset i am using is mez01.j2t. thanks