Jack Russel Terriers are small and they can jump high but not too scary. If you own a miniature Yorkie then yes he is a beast but for the most part the post man just smiles at him and gives him a pat on the head. I find it hard to believe he is scary. When we first moved in we noticed after leaving the house sometimes that he had dug a hole under the fence and gotten out. We tried this green plastic fencing at home depot and he just chewed through it then we resorted to buying bricks and placing them where ever we found a hole. We also decided it would help to not weed wack in front of the fence so the grass would grow tall and further deter him from trying to get out. We sat him down and had a little chat with him to see if he was happy in our home and maybe thats why he was leaving but he didnt give us much to go off of. I don't know why he keeps getting out but my best guess would be he sees rabbits and squrils and cant help himself. He is well fed and can come and go as he pleases with the doggy door. What more can I do really? (thats a rhetorical question). I have four kids we leave the house to swim and pick up milk. If I notice he has escaped I walk the fence and cover the hole.