Ok. Right now I've 2 ways in my head, either you try to hook TE_WORLDDECAL/TE_DECAL with register_message() and block them ( don't forget to check if it's the right decal index ) either you can block directly UTIL_DecalTrace() or UTIL_GunshotDecalTrace() calls but you would need Jaoquim's module ( Sigscan ) but it's not finished yet, he has to make the hooking stuff. In waiting, try the first.