What rehab instructions did you get? Generally with something like this you want to focus on long & low and lots of straight lines while avoiding much bending, circling or spiraling. Neck injections can be tricky and need to be done with a lot of care. Personally I’d talk to the vet about trying adequan or pentason to his program before trying the neck injection. They can help him and will generally increase the lifespan of the injections you’ve already done.