Ok so you missed this

The Bite Stops Here

We have always worked on ignore the bad behaviour or use distraction tactics and praise and reward good behaviour.

We stopped all the treats apart from cheese and chicken and swapped her from puppy food to adult,spent alot more time one to one training.We used distraction methods when she was doing something she wasn't supposed to be doing.

I was pulling my hair out with her she was so naughty,but the one to one paid off and a few months later she was alot better.

I would suggest not grabbing him by his collar as you may be hurting him and he maybe snapping as a result.When you move him make him sit and reward with praise and a treat - so it's positive reinforcement.
Same with the hedge show him a treat and call him praise and reward,after a while don't give a treat all the time,make it random.You could also use a training line when he's out side so he can't get under the hedge.

Terriers can be fiesty and very stubborn.
Hope this helps,remember patience and time,it won't happen overnight.

And yes i do have better things to do but if you insist on not listening and keep asking the same questions (or different Qs that have the same answer ) then i will keep posting because im concerned for this puppy and i think what is best for your dog (remembering that the dogs needs come first over your own) that he should be rehomed. MHO

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