mm writes:
If you're burying it when you're done, silicone tape, I think it's
called, is even better than heat-shrink tubing and doesn't slip on, it
wraps on. Stretch it to 2 or 3 times its length, then wrap while
streched and within a few days it merges into one big probably
waterproof blob. Hard to find though.

HD has it in several locations in our local stores (plumbing and maybe also
electrical areas) - may be hard to find cuz most people don't know about it.