What about not deploying to a server that is resolving their DNS until payment is complete?

When final payment is received, final deployment occurs. Until then, it can be accessed via a URL you control.

Otherwise, if you're really looking for something like that, I'd suggest https://forwardhq.com

I was under the impression that the main concern is theft of HTML/CSS/JS sources without payment. Anything that allows access to those files would still be vulnerable. The idea was to have the site rendered real-time in the cloud and transmitted so that no source assets could be stolen.

Apologies, I believe I interpreted the protection for freelancers a bit more broadly. Rarely have I seen/heard of clients who have resorted to blatant theft of the sources without payment. They usually just try to get away with using the sources. That is no different from theft, in my book, but it seemed going so far overboard as to obfuscate/hide it all vs. just getting oneself a proper attorney and initiating legal action would be better. Better yet, get an attorney to draft a contract that you can reuse with [nearly] all clients.

I was speaking more to sensible protection--do not deploy & resolve DNS, do not transfer source code ownership, do not relinquish copyright ownership, etc. until the final invoice is paid. And make sure it is written that way in a contract and that the client signs the contract before work commences.

I'm not sure how you can do that from a technical standpoint. If it's on my screen, I can view the markup.

Check out browserling

http://browserling.com

Many clients don't know anything about viewing markup and recreating work. Especially if there is something powering a site/application on the server. The HTML doesn't help them much.

Think of something like VNC over WebRTC or Flash. Just rendered frames, no raw access to the source.

Many clients wouldn't find this sufficient for user acceptance testing.

Won't any mildly tech-saavy client want to try it on their laptop, phone and/or tablet to make sure it looks right in different browsers? Well, it'll look exactly the same, because they aren't actually rendering it....

The minify/obfuscate solution seems sufficient (and possibly an expiration date...) but even that would be obviously unnecessary with many clients.

It would be interesting if you could render a Flash depiction of a live website and allow interaction without degrading performance or having it "look like Flash."