I think eight feet ought to be deep enough.
That would certainly be nice. Short of an active volcano, I can't think of a hole deep enough that I would want to drop him into.
Sadly, one of the numerous ugly aspects of his existence is the requirement of nursing assistance whenever he relieves himself, due to his hooked hands.
UK papers have described this as "the worst job in the world" as I recall, and that sounds about right. Despite his disabilities, he appears to focus all of his and his supporters' energies upon milking the system and causing trouble in any conceivable way. He views his incarceration as an opportunity to continue his war upon the West.