"Is it spring fever?" she asked.
No. It is definitely not spring fever.
The first question to ask yourself if you're encountering such a problem is, have I done any active training, using a positive reward method, to teach my dog that he's supposed to stay in my yard?
A dog does not inherently know that his territory has boundaries. That's the first thing that needs to be taught. Secondly, he needs to be proofed against any and all distractions that he may encounter while in the yard.
What do I mean, proofed against distractions? Well, how about rabbits, deer, birds, other dogs, cats, people walking by the road, etc. If he saw a rabbit in the backyard and it took off running into who-knows-where, what would he do? Dog law says he'd probably chase it. That much is inherent. And so, you have to train against it. Usually, you do this with a recall command. And remember, whatever you're asking your dog to do has to be more attractive to him than whatever it is you don't want him doing. So ask yourself, does coming to you for a dry dog treat compare in the least to chasing wildly and freely after a bunny rabbit? Probably not. Chasing a bunny is probably a 10 on most dogs' scale of awesome things to do; getting a dry dog treat from you in exchange for coming when called is probably like a 4.
This means you need to activate the prey drive in order to train against the prey drive. I followed instructions in Culture Clash (book by Jean Donaldson) and used a brand-spankin' new toy — a stuffed animal rabbit, just to be cute! — to train the recall. I put Sensi in a sit-stay, starting at about 5-feet away from me, and when I called him to come, I spread my legs out (and brace for impact!) and tossed the toy through my legs and behind me, creating a tunnel for Sensi to run through in order to chase after his toy. Now, you're activating the prey drive while teaching the recall command. I gradually moved him and practiced at different distances. Then, I'd surprise him while he was just moseying around in the backyard. Then, we practiced the same exercise in the front yard, the side yard, etc.
But there's a problem with this training, and that is the fact that it relies on your presence to call the dog. If you want to be able to just let your dog outside and feel confident he'll stay within the confines of your yard, it's not going to help. You can instill the strongest recall in the world, but if you're not there to give the command, the dog is going to do as he pleases.
Personally, I'm not sure it's possible to proof against every distraction that could possibly show up while in the yard. You can't control the world outside your house, right? So how can you be sure you've proofed against every possible situation?
Because of this, I do not condone the theory that you can just let your dog out to do his thing, totally unrestrained, and trust him to follow human rules that he really doesn't know and hasn't been taught. If he spots a person walking a dog in front of your house, how is he supposed to know that it's rude to walk over to them and introduce himself? How does he know that he's not supposed to follow that scent of rotting flesh from a dead raccoon deep in the forest? He doesn't. He just doesn't.
Fortunately, there's a myriad of solutions out there to help you keep your dog in the yard — fences, zip-lines, chains, invisible fences, etc.
But, why is that Eddie is doing this now, as a 3-year-old, when he has no history of doing this before? It's hard to say why, but this is something I often try to express to dog owners: why matters very little. Why is not necessarily going to let you know how to fix the problem. What you think may be "why" may have nothing to do with the behavior problem at issue anyhow, and we can't really check with our dogs to find out whether we're right or wrong. So go ahead and muse about the "whys" but understand they're not critical. The critical element is finding a way to fix the behavior problem. Why the behavior problem exists may or may not be something you ever figure out, so it's best to put that question in the rearview mirror and drive on forward for the sake of solving the issue at stake.
Either way, the fact that Eddie is not neutered is going to contribute SIGNIFICANTLY to whether he can learn to stick around. Non-neutered male dogs are the most likely to roam and the most likely to cause trouble while they're out and about. You cannot turn off the sex drive on a non-neutered male (unless you neuter him, of course!) and being as such, he has an inherent, instinctual need to find a mate. And dogs will travel miles to find one.
In addition to this, you have take breed into consideration. He is part Jack Russell and all terrier and what does that mean, folks? He has energy that will never wane, a fierce independent streak and a strong prey drive. This is a breed that needs not just daily exercise, but VIGOROUS daily exercise. He also needs some good mental draining exercises too to satisfy the independent hunter in him — hide and seek in a sand box (bury toys, make him find) is an ideal exercise for these breeds, which originally were used to dig varmint out of the ground. Treat dispensing balls, hide-and-seek with treats inside the house, agility and similar activities are also excellent outlets for these dogs.
I've known at least one person in my life who has adopted a Jack Russell, only to find they can't handle the breed and wind up giving it back to the shelter. Don't let the size and cuteness fool you — these guys have some serious energy. As always, the first step in improving your dog's behavior is to make sure its needs are met. With a Jack Russell, that can be a challenge.
Of course, nothing is impossible. Check out this story about a North Oakland woman who trains her Jack Russells for agility: Stray brings home luck
And, here's some previous posts about why it's so darn important to keep your dogs in your yard:
Another good reason to keep your dog in your yard
Don't let your dog go
Does anyone use a leash?