How old is he?
If you keep building the walks up, lots of 30 min, decreasing to fewer but longer ones,
do you have some calm clean water nearby, that you could throw sticks into, water is a great way to build up stamina,
has the dog been de flea, up to date with front line or stronghold?
best comb, will take out under hair
borrow one of these, brush out,you will get loads out, give a bath, to avoid shaking wash head last,
I use ecover washing up liquid, it's so mild and harmless, works very well, doesn't irritate,
treat for fleas, keep dog dry for 48 hr after treating,
happy dog,
you sound like a good friend, I bet the dog won't want to go back to the boring life, good luck.