Is a website design eligible for copyright protection

I want to give my website design clients the copyright to their site after they have paid their invoice in full.

This will be after I have installed the site on their hosting account so if they decide not to pay they can technically keep the site

I want to have some legal right to my creative work in case they renege but I want to relinquish that right once they pay.

Is this possible?

One way to protect your self is with a written contract between you two.

But best is if you can somehow have a control of the website in case they do not pay.
Maybe you can encrypt all of the code and make the site render useless if they do not pay.

If you did not do the work under a “work for hire” contract/agreement, you own the copyright even if the website is on the clients server.

As mentioned, you would want to put the transfer of the copyright as a clause in your contract.

Basically in short, the clause will state that when the invoice(s) has been paid, you will transfer the copyright to the client.

What’s more important is how would you take advantage of retaining the copyright? Sue them for copyright infringement?

I would suggest scrutinizing your business process and coming up with solutions that don’t rely on a threat of a copyright infringement lawsuit. Signing a good agreement in the beginning of your contract is usually sufficient to ensure that the client pays - also, should things go sour, that agreement would be a much better basis for a breach-of-contract lawsuit than a copyright infringement threat.