Trial period possible?

Just wondering if anyone out there knows of a way to write html code that
will effectively disable itself after a certain time period?

Here's my situation... I have made a small web site for someone, but I don't
exactly trust them to stop using it (in the event that I am not paid for 
the work)
Is it possible to set a "trial period" so that he will no longer be able to 
access/use it
without my permission?

Silly question, I know... but I really don't have a clue!

Thanks...

Cleo...

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