I have 2. They will both get out if they get the chance.
However, 1 is far better than the other and I never did find out exactly which parts of the hedge he was getting through. He never used his sneakier holes when I was watching.
In the end I resorted to an electric fence off ebay, (no doubt this will cause cries of disgust from some members on here, though the fence is there to protect him.), however, after he had invesitgated it once or twice he won’t go near it. I waiting for him to work out the batteries are flat and we can get through painlessly.
I think that all terriers have an instinct to “work” hedges, looking for prey and this leaves to their Steve McQueen impressions.