Jack Russels are awesome! I've got two of them (a Parson Russell named Teddy, she's 5 months now) and the one on the drawing (she's almost 2 years). They're so full of energy and they want to play every moment of the day! It most have been awful to bring your dog back to the shop, wasn't?
It was, when we let our Pomeranian and Jack Russell off the leashes for the first time, the Jack Russell grabbed our Pom by the neck and wouldn't let go, yet at the pet store they said they would get along and we trusted them.