
If you're using human grade glucosamine & chondroitin, then you have to make sure your dog has vit C in their diet, as (with many things) vit C is needed to allow them to absorb the vitamins and minerals, the same as us. Otherwise it isn't as effective; I give Indie one human grade tablet twice a week, as mine are on barf, they get raw blended veggies regularly and so she will be able to absorb it more effectively than without any vit C.
Other supplements are devil's claw and green lipped mussell extract, I've heard good things about both, although never used them myself.
I also put into their blended veggies apple cider vinegar (one cap for enough for a fortnight) and turmeric (one t-spoon for enough for a fortnight) both of which promote healthy joints. Mine also get tinned fish in either oil, or tomato juice once a week, although the tomato juice will contain a small amount of solanine, lycopene, the stuff that makes tomatoes red, is a very effective free radical, and although Indie has arthritis in her knee and possibly one of her shoulders/elbow too, it hasn't exacerbated the problem. But I would avoid giving any of the nightshade family with green parts, so green capsicum, green parts of tomatoes, any part of an egg plant, and green parts of potates, you get the idea, as these are rich in solanine which can exacerbate arthritis.
You could also try a bio-flo collar, again, I've heard good things, although with my own experience it didn't help Indie much, if at all.