Teleport is basically impossible to stop completely because to the server, the client is always issuing teleport commands. The only question is how far are you teleporting? A server model is in theory safer against other things you might want to do with your client, but it's not like other MMORPGs are plagued with hacks. In a game with very rigid rules, it's pretty hard to successfully lie to the server for prolonged amount of time. For example let's say I hacked my client to always report 'I just healed myself for 9999', and let's say server is completely trusting here and doesn't even question how this is possible. It's still hard to do anything else useful because if I ever start trying to cast any offensive spell, the server is going to notice I somehow casted 2 spells in one GCD and will suspect I'm hacking. About all I can do is stand there and never die.