to make a block that players can't shoot but can stand on, make it a func_illusionary. Then copy paste that same block, texture it with player clip, move it to world, and then place it on top of the func_illusionary block. Alternatively if you want to make a wall that you can't shoot, it's easier to copy that wall, make it 1 unit thick, place it over the wall that you don't want ppl to shoot, texture it with skybox, make it a func_brush, change render mode to "Do not render." this way you don't get a leak if you make the wall a func_illusionary. there's also something called a func_speedmod (or some shit i cant remember) which you can use to make it so that you can't even shoot your rocket launcher at all or detonate stickies (this is used in coop_soldierbuddies and jump_emulation for instance) in a certain zone.
hope this helps, im in a rush, so cant explain it further
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