I am wondering if anyone knows how to limit NAT Connections using iptables or some other command I have not thought of yet.

Basically if I have 10 users and I am using NAT I only want each user to be able to make say 100 NAT connections and if they exceed that say have 101 connections then their connection is either dropped unitl they fall below the limit or their connection is stopped until administratively restarted again or for a time limit. Any help would be appreciated?