Yes, they will spawn once per in-game day forever, but only if the previous spawn protecting that chamber has already been killed. They are generated by a spawner, not as part of a field mob, so I'm pretty sure that workbenches will not prevent it (haven't tested directly yet, so take this part with a grain of salt).

Workbench should prevent the spawn. I've built a big castle in the BF that included a chamber and I never got a spawn there while the area was covered by workbenches.

You can mess with the terrain just a little to keep him stuck. You can also mostly bury it to both hide the site and keep the spawn out of trouble.