Sometimes I walk my dog off-leash, and he is pretty well behaved for the most part. That is until I try to approach him with my hands, say, to put his leash back on. He will immediately dart away from me when I do this, even though he walks by my side most of the time anyways. It's really frustrating when he does this because I am usually trying to grab him to avoid a dangerous situation. Plus, I know he is just doing it to be playful. What can I do to correct this?