I don't know about rescue dogs but a local vet told me that they have had very positive results with anxiety-wraps (elastic body-suits for dogs) as a general aid for reassurance (not just anxiety) which might work in terms of allowing you to touch his neck/collar? Just a thought...x

A potentially very useful thought.....I use a thundercoat and it does help

When I got Bailey at 7 months old, a collar scared him to death, he didn't bite just hit the deck and pee'd himself I think he associated having the collar on with 'bad stuff' as he was quite badly beaten and trained with a horse whip from what was said in the rescue

I started off with a slip on lead and a bit of string. The lead went very loosley around his neck only when we went walkies and the the bit of string and me spent hours together starting with hanging it off his nose - treat and tummy tickles until he relaxed, take it off. Put it back on -treat - tummy tickles until he relaxed when he was fully relaxed having it just on his nose we went further up so it sat on his forehead area same again treat, tummy tickles . . . . .. until he was relaxed with the string, we then moved onto a lightweight collar, then a proper one

It took nearly 6 months for him to be able to function normally with a proper collar on constanlty, the only time I put it on him fully for months was when we went walkies as I needed him to have his tags on.

He's fine now with anything being put around his neck but it was a long haul so get ready for it

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Many thanks Sled Dog Hotel for a very helpful long post. Have ordered Adaptil and Kalm Aid.
He's generally much better now we are avoiding stressful situations.
Still can't take off lead and collar or put on harness. But thought I try again after the products start working.