Instead of changing his food, you could just limit how much he eats. I dont know whether you free-feed or if you feed on a schedule, but feeding on a schedule would be an easy way to lower & maintain his weight, because you'd know exactly how much he's eating.

With the toys, my dogs do the same thing. They've destroyed the 'indestructible' Kongs and Nylabones and even Rhinobones. The toy that seems to last is a purple squirrel that I got on Amazon. It's been almost a month and it just barely shows any damage, even being chewed on by three large dogs. Some dogs are just more determined than others to get the job done. I'm not sure if they'd be too big for your dog, but racquetballs seem to hold up well too. 3 in a container for $4 at target/walmart.