The best ones ive seen are the little mesh type silver or black pencil tins.
You can pick them up from a cheapshop for $2 - $5 depending on size.
They are made of thick metal and wont bend/break, the metal doesnt heat up too much - so your snake wont burn itself, they still distribute the heat well, the holes are small so if you have a hatchy, it wont get thru and they last forever!
Stick it over your light and put 2 screws through the top to hold it on.
and you're done

Its a bit of a pain unscrewing it to change the globe, but that doesnt come around often.
thats the only issue ive had using them.
Good luck!
this sort of thing, but taller and without the pins in it... lol: