We do all our contracts with ACH evergreen plans (Means they do not cancel without a written cancel from client)

We just list out what services we will provide to them, the hours of which each service is available and the numbers they can call

It also clearly describes that this does not cover on-site support and that on site service is billed on its own invoice

Its a one page document that at the bottom has their signature and a bank routing / account number box

-Branden