I was going to bed but...
Make the brush a func_wall entity. Texture it and go into it?s properties. Put the "Render mode" to "Solid" and "Render FX" to 255. This will make all the blue parts of the entity to be transparent... If you set it to "func_illusionary" and put a clip brush in the same place of the fence you will be able to shoot through it too!!!.
Same is applied to ladders in the brush part of them. You make the brush part "Solid" and "255" and leave the "Func_ladder" as it is. This will work... If you use illusionary and so on you will be able to shoot through ladders too.