Decal render only one object at time

Hello guys, I'm doing one fps game and when the player shoot i made a decal of the wall shooted, this decal is one cube. My point is, when the decal is in the floor or wall it Works fines but when i pass over this decal's cube with my player the material of decal render my player too. What can i do to my decal's cube only render one object at time? Thank you.