As an aside, I love Jack Russells. I had one at 3 weeks old who had been abandoned my his mother (but that's another story).
I had him for over 17 years - or he had me. He had his 'own' chair', and if anyone else dared to sit in it, he came and stared at them until they moved. He was such a character - ruled the house, was always up to some kind of mischief, was great with children, later developed selective deafness and then cataracts, and had to be 'herded' by my lab.
I was overseas for a long period, and he died the day after I came back - I like to think he waited for me.
I hope you and your little friend have such a rewarding relationship.