the way AP makes lamp cut outs for their PVC cages is easy and looks great (I would make a square cut out instead of a round one to make it easier but the same principal still applies:
basically it is a sandwich
Top of enclosure
screen
PVC retaining ring (could be made from polycarb or wood)
screw it all together and you have a screen for you lamp that not only looks good but is 100% escape proof (at least as long as your BP doesn't know how to use a screwdriver lol)