If your just wanting to disable ping for certain users, do that. You might want to look at this.
Essentially, just run :
su -c "chmod 700 /bin/ping"
Now only root can run it. You could also edit your users PATHS. Maybe you mean to stop icmp packets ? Ping is a very useful command I think. If you want to stop "ping" packets, your really wanting to stop icmp, right? If your trying to edit /etc/sysctl.conf, you will need to reload it after you do so.
Any way, 8p.