Maybe I'm making a large assumption here, but since you're doing web development you presumably have access to their site. Why not just remove your code from the site until they pay you?
In my contracts, it states you will not use the work until we've received payment, and we will unhappily file DMCA takedowns against infringing users who've not paid for work done which isn't theirs yet but they aren't paying yet continue to use. (As we only transfer rights to the work upon final payment).
After a certain (long) period of no payments, we have a forfeiture clause, which removes all right of them to ever use the work without removing the debt for items already performed. This works considerably better than interest.
A TRO is a much cheaper thing to get than a small claims judgement.
For most clients, we additionally do not provide the source code for them until they've paid in full.
Also, a reputation for destroying clients' web sites isn't going to help. You won't get far enough to explain "Yes, but…"
"Why not just remove your code from the site until they pay you?"
I thought about that, but one has to be very careful about that, or one stumbles into illegal territory.
Also, it is complicated, there were several programmers working on the site, and none of us owned any portion of the code, by which I mean: each programmer was free to edit any portion of the code (which is an awful idea - the code quality was terrible because no one had any sense of ownership over the code).
I signed an agreement with MyBailiwick (Miles Spencer and Todd Carter) which said I owed the copyright on my work until I was paid, so in theory I still own some partial copyright, but my code is mixed in with the code of every other programmer, so it would be tough to enforce my copyright without tripping over someone else's code, which might in fact have been paid for.
More so, I was paid for the first 2 months of work I did for them, it was only the last 6 weeks that I was never paid for. So even among my code, it would tough to say which parts I was paid for and which parts I was not paid for.
In saying that upon payment it is a good idea to have a routine that kills the check to your server as an authorization check that fails in production could shoulder you with a good deal of liability.