heating for outdoor florida enclouser

[ilovelizards]

I live in central fl and we are working on covering a old padeo porch into a tegu enclouser well most of it .We are bricking off the mulch so we can have a walk way to go from the house to outside he will be feed in his bowl in this un mulched area .He will have a pond with a water feture&live fish,plants,a over the foot brige,mulch ect we were planing on makeing a heat spot over a huge stone any ideas on how?
He will be wintering inside and taken out for walks events and handling when awake.