He's only just over three months old. A five-minute attention span is amazing at that age. My pup, now 13 months old, had a span of about 30 seconds at that age.
I've raised three pups in the last 10 years. Two of them were high-energy golden retrievers from working lines, and they were worse than what you're describing. My last Golden broke furniture and ran clean through a (closed) glass door to get at a squirrel, before she was 6 months old. My current pup has (so far) broken through screen doors, jumped into a frozen swimming pool and wrecked a folding crate. Pups are a LOT of work, especially if you have a feisty, active one, as seems to be your case.
If he's doing stuff he shouldn't, you need to restrict his freedom (crate or tethering to you). He shouldn't be allowed to "stalk the house". He's clearly not mature enough to have earned his freedom yet, so he should either be with you and under control, or in his crate. At 13 weeks of age, there's no "in-between". My pup is 13 months old and still doesn't have freedom in the house.
If your pup asks to go outside, let him go once, but go with him and make sure he does his business. He should go out to pee, or to play with a human, but he shouldn't be left to roam. If he can't be trusted to come back, take him outside on leash instead of sending him on his own. If you let him roam, he'll ask to go out all the time because he's having too much fun doing his own thing.
If he barks at you while you eat, put him in his crate in another room. You don't have to tolerate pushy behaviour.
The harness may help with walks, but training is key here. When you go for walks, fill your pockets with kibble or treats, and reward him constantly for not biting the leash. If he bites the leash, immediately change direction - do an about-turn and walk the other way. He'll have to follow and won't have time to bite the leash. Reward him for following. For a while, you may be walking in circles, but it will get better, I promise.
You're in charge here, not him. Don't pander to him - give him structure. Think of him as a toddler. You wouldn't leave a toddler on his own in the garden, or free to roam up and down the stairs, and you wouldn't give in to tantrums either.
Training a pup doesn't always give immediate results, but you will start to see some results in a month or two. The first six months of a pup's life can be rough, especially if you have a feisty one, but things will come together eventually. You're doing a lot of good stuff. Just keep it up and be patient.
Ruby 13-01-2007 to 18-03-2015.
My dog of a lifetime. I'll miss you forever.
Last edited by ceegee; 01-11-2017 at 12:22 PM.