There are many different ways to implement lexical scoping. Here are some of my favorites:
If you don't need super-fast performance, use a purely functional data structure to implement your symbol tables, and represent a nested function by a pair containing a pointer to the code and a pointer to the symbol table.
If you need native-code speeds, my favorite technique is described in Making a Fast Curry by Simon Marlow and Simon Peyton Jones.
If you need native-code speeds, but curried functions are not that important, consider closure-passing style.
