Just for temporary quietness - and being not so noticeable - perhaps a short piece of clear nylon tubing which can be bought at an auto parts store could be slipped over the hook part. It would be contained by the gate so it wouldn't get away.

I think the swivels are meant for carrying the rifle to the hunting spot, then it is quickly removed when the hunting actually begins.

I do make these swivels in batches. I don't keep any inventory, as all my accessories are made specifically to order. I'll be doing some in May - probably till I'm cross eyed and have to go work on something else for a while. Like a truck.