Ive had terriers for years, I wish you luck!! :-)
Intensive training so that your dog returns when he is told without a problem.
I actually nearly lost two Jack Russells like this.
They both managed to escape and went hunting in the fields and wood up behind my house, they were both gone for two days, I scoured the woods every spare minute I had. The dog returned severely bitten around the back end and needed emergency surgery, the bitch was never seen again. The vet assured me that the fleas found on the dog was from a badger! They obviously found a badger set, the badger would have killed the smaller bitch.