An oversized mongrel afraid of the dark with too much bull in the mix, no nose, a Sealyham which was a white Lakeland with dachshund x, and throw in a red fell and some mini-bull, sold to the highest bidder.
Sad to loose a pup by accident like that.
Not sure after a pup dying by accident after getting hit by a car why you would question how you could kill something now? Pests need controlling and the countryside needs to be managed. The alternative is snaring, poison, trying to catch with not more than 2 hounds or shooting? Controlling with terriers to me is the most humane control technique.
Terriers and terrierwork can be a tough game without accidents. If it's for you get another but take your time and go after the best of breeding you can possibly get and watch out for spoofers as was
Physical side is easy. Just feed them decent grub and give them plenty of exercise.
Mental side is more difficult when started off badly and depending how old can last a lifetime!
Expose them to as much different noises, smells and sights as possible. Patience is a necessity with backwards ones! Sometimes deeply annoying and frustrating to deal with.
I was always fond of the underdog myself, so fair play to you. I sometimes wonder about some working dog men who think dogs are machines or simple tools? Bit more to them than that if you want to get the best out of them.
Best