Sedatives for dogs?

I found a few natural sedatives online,but am unsure what companys are reputable.I have a 3yr old corgi that was dropped off to me about 2 yrs ago.He has alot of issues,I changed his diet a few months ago to only natural food and he has changed so much for the better.When I can afford I want to make all my dogs feel that good.But this poor guy was badly neglected and I think the woman involved was abusive to him.
He will let my bf touch him more then me.He plays sorta,looks for attention from me and lets me touch the top of his head,I just cant touch him anywhere else or he flips out and trys to bite me.I admit I am scared he is going to bite me,he does not back down,and I dont want to show fear but I also dont want to make him hate me or over excite him.His nails and hair needs some good TLC.I figured if I could get a muzzle and sedate him,maybe I could work on that without upsetting him.
Any Suggestions are welcomed!!

Have you gone to a behaviorist and/or trainer? Positive training methods and calming methods may work. It's just going to take a lot of time and patience. It will be more benificial than drugging(weather natural or not).

Finding a good dog trainer could help this. It's the most natural way of calming the little guy down. He'll be much happier too, rather than having sedatives... they affect different animals in different ways and alter their personalities sometimes A LOT.

A trainer that is right for your dog, and knows how to properly correct the negative behaviors will be very effective.

Good luck and it's never too late for abused animals. They are sensitive and need some extra work but they are the ones that need guidance the most.

Editing this- I meant to quote Miss Marie and say that is exactly correct!

Thanks so ,much for the advice,never thought of a trainer for the situation.