Layering issues

Executive summary: Its a pain!

Slightly more useful suggestion: search forums for "Guitar" - there have been a few threads and different ways people have looked at.

As you have no doubt discovered, if the arms are independent, life is hard because the hand must be a child of the arm, but the hand has to be in front of the guitar (so cannot a child of the arm!). It looks like you want the arm independent from the screenshot, so I am going to proceed on that assumption.

Easiest suggestion I have:

• Use a swapset to have two left arms - one for normal moving (but which cannot move in front of the guitar), a second one for playing (more on this second arm in following points).
• The trick is to make the second arm in the swapset the upper arm only (so its only a stump) and NOT independent. While strumming, the upper arm does not move, only the lower arm (and hand).
• Because the upper arm is not independent, you can now add the lower arm and hand in front of the guitar lower down under the Body layer, and they can be independent. It can attach to the upper arm stump because it is part of the "body" mesh. Moving the lower arm will not move the upper arm segment (its fixed), but the lower arm can move up and down to strum etc the guitar.
• The other part of the trick is the lower arm and hand also needs to be added to the swapset trigger for the upper arm stump, so it appears and disappears in sync with the upper arm.

Oh, if you see any videos from @k_oshiro  when searching the forums for Guitar, he often has great videos he puts together for these tricky situations. I would definitely check them out if you see any. (And check out I think its "martin" from oksamuri - he has a guitar player as well.)