Your in for a lot of work if you want it done now. Fill a 5 gallon bucket with sand and stick the mailbox in there.
Also agree on calling ONE-CALL. When we were living in one of our past houses, I was building some sitting benches for the kids in their sand box and dug right through my phone line. I was all worried about all the money I was going to have to spend and the trouble I was going to get in.........
and then I got my tools and electrical tape, spliced it back up, taped the living crap out of it and it worked great for as long as we owned that house....
Now when I hit the telephone junction box in Hampton Iowa when I managed the elevator there and destroyed service to half the town, now that was another story. Good thing I knew the telephone repairman or I would have shelled out big bucks for that one.