How restrictive can you safely be on your post-termination clauses with regard to a) length of time they apply after termination b) distance around your office that you prevent them working in a similar business in and c) who you can prevent them working with eg clients, other employees, third party suppliers who they came into contact with etc

I know if you go too far the courts just throw the whole clause out rather than amending to a more reasonable approach.

Any tips / thoughts from previous experience would be gratefully received.
Jules Parkinnen