Then how about this, with the current system this will be the addition that can be implied to yours,
Checking their IP ADDRESSES. If the network's IP was already used from registering then it won't be used anymore. Certain programmers can only work on many IPs so its impossible for them to use many addresses just to create a new one.
Although we implement this "If the network's IP was already used from registering then it won't be used anymore." people will still find a way to create new accounts for farming. They can use other devices to register new account or even use VPN to protect or hide their IPs.
Actually it is not prohibited to create account using the same IP address. If ever that a certain IP address has been already used to create a account, we will just need to pay a little fee so that we can be able to post using the new account created with the same IP. It is not prohibited to create account as many as you want (as there is no rule about it if I'm not mistaken), the main reason why Moderators restricts us is because we are abusing it too much.
We can freely create accounts if we'd like because it is for free, but because of some exploitative peoples, farmed account existed. Without these abuser peoples, our Forum will be a peaceful Forum for sure.