Please implement asymetric encryption to all commands passed though network to avoid players to issue own hacking commands.
System could work following way:

1. Server will generate new public and private key on server restart
2. Client will connect to server and download his public key
3. All commands used will be encrypted using servers public key and decrypted on server using his private key.
4. All commands issues by server are encrypted by servers private key and decrypted on client using servers public key
5. Limited list commands as chat will be not encrypted
6. advantages: player won't be able to teleport easily or hack without knowing how to encrypt using proper key from server
7. More commands can be executed client side without verification by server therefore less networking traffic, less server overhead and better ingame security.

Also calculate players movement statistics clientside and specify max range via walk, drive and fly per 5 seconds. If average number will be more then max, then it can be considered as hack without checking serverside