It sounds like he's a tweenie, almost a mini, that's good.
It was wonderful of the shelter to save him and pay for cold laser, and of the rescue to pull him and foster him.
I do not know if it is an option, but the rescue might be willing to put you in touch with the foster so you could get a more complete history on him. The foster may be thrilled to meet or email with you and tell you all about him. And the foster the rescue gave him to may have been a medical foster, or a very experienced foster (or may not). Also, if this was a breed rescue (a dachshund rescue), they may have more experience with IVDD dogs than a general rescue, and the vet they use may be better informed about IVDD dachshunds, but IVDD does affect other breeds, too.
Another thought is, if the rescue is local, and if the foster says the rescue vet has experience with IVDD, you might consider trying out their vet for this one particular pet, while continuing to take your other dogs/pets to your regular vet? Just an idea, thinking out loud. If the experienced vet can assure you that Peanut is fully healed, then your regular vet could probably provide his other routine care. Some dogs will have a second episode of IVDD, but the majority will not. (Again, it is helpful to address things in his environment like jumping off the bed and running up and down stairs, rough play with other dogs, etc. to try to protect him from further episodes.)
It would also be good to know where he got the cold laser, as I don't think that is available everywhere. At least here I don't think regular vets all have it. He may have been seen by a rehab specialist, I have no idea, it would be something to try to find out. You have a lot of unanswered questions it would be interesting to find out!
As far as I know, and I am not an expert, one important thing is whether he has any
signs of pain at all. If you can't get much info from the rescue and don't want to try another vet, this is pretty basic and may be something your regular vet could determine. Or you may have a sense of whether he is completely pain-free yourself. Pain could be an indication that it may not be fully healed.
I'm giving you my
, but you have kind of a unique situation, not knowing his full history (he has passed through several hands) and you might consider asking how they would handle this situation on Dodgerslist. They are considered to be reliable for best practices in caring for a dachshund with IVDD.
If you can establish that the disk is indeed properly healed, then I would highly, highly recommend water therapy to strengthen and improve his walking. Hydrotherapy can be done at a canine rehab facility, or it can be done free at home with a dog this size. Here are some links about hydrotherapy.
http://www.abledogs.net/poppy.html
http://www.dodgerslist.com/literature/watertherapy.htm