[TowerTalk] Coax questions

[r miles]

I have a few towers scattered over 2 acres in the back yard. All have  coax runs buried in PVC. I'm planning another antenna out  amongst them. I have a general idea where all the runs are buried but not to the exact inch. I can just start digging  lightly to find the PVC but that's a long process. Is it possible to use a metal detector? Something like the beachcomers use.The PVC is about 4''-6''  below the surface. Frost line is not a problem in the Tn delta.  Has anyone used one to find coax? 
Is there more than BuryFlex on the market? I just want to consider what will be best. This will  be an HF run so no worry about VHF/UHF losses.
Please contact me off reflector to make it less crowded.
K9IL