I need help! Stubborn dogs.

OK...we live on 12 acres of woods, surrounded by woods, pig wallows (=pig hunters with their vicious dogs, wild pigs etc.).

We have two sisters: Thelma and Louise 3 years old...mother is a Chesapeake Bay Retriever father is a Labrador Mix. Both have been thru obedience school, both sit,stay,down etc. on command. Lovely dogs...we are doting parents...they are spoiled. Their "kennel" is 1/4 acre orchard but they are mostly with us in the house or on the porch.

PROBLEM: for a while the "escapes" happened once in a while...now the two of them are bolting every day. It is as if someone yells "Surf's Up" and they tear off, unresponsive to calls. Today we put the shock collars on them, set them up for them to "run" and they did. We hit them with 4s which they yelped at and ran right through. They go off, who knows where...wild pigs kill dogs, people steal dogs, pig hunters shoot other dogs...

We are desperate. We are faced with the alternative of keeping one on a leash at all times (which is a handicap for US as we are working the gardens) or keeping them penned up.

Can anyone suggest anything? Any animal behavioralists?

It is as if them have become addicted to the "chase"...

And we are ragged....

TIA - Mahalos