They sell a type of top that should help with escapee snakes.
http://www.novalek.com/terarep/teratop.htm
It has velcro that goes around the tank, and the screen velcros to the side of the tank.
ALso you can try this Zilla makes a locking/sliding screen top which could also help.
http://www.zilla-rules.com/products/critter-cages.htm