sebastiantombs
Known around here
Putting a splice underground and not in a watertight enclosure is a little iffy, to say the least. I'd say to leave a loop, say 3 feet, of cable on both sides for repairs if needed. Wrap the whole splice, and a few inches onto the cable with a couple of layers of high quality electrical tape, 3M 88+, then add a layer of coax seal, or other self-amalgamating, tape past the electrical tape, then coat the whole thing with a few coats of rubber based paint well past all the tape. This may seem like overkill and a half but if water/moisture gets in there it'll mess things up pretty badly.