Actually forcing all customers to acknowldege that they have reviewed and agreed to abide by the host's TOS by using a checkbox before they can sign up is pretty iron clad under the new laws relating to internet commerce.
It's the same as signing a contract. You can only get out of a contract under limited circumstances which are too numerous to detail here.
The key is forcing them to check the box and having a link to the tos next to the box!!