We routinely send home on pain mangement for spays and castrates, but we don't give Ace.We give Rimadyl which is an anti-inflammatory as well as pain relieiver. Most post sx issues with spays-sutures chewed out, and the occasional bloody scrotum from castrates. We don't suture castrates and really don't have many problems with them healing. My own dog managed to chew out 2 stitches just after waking up from sx AND then my DH takes off e collar while napping with Sally who then procedes to remove the rest of her sutures 5 days after sx.
I heard about this for a lonnnnnnnnnnnnng time !!!! Fortunately she had healed enough that she didn't need a repair on it. Sounds like the meds could be too much- you could give half the amount a try if you thinks he needs it...sometimes if they are feeling pain they will lick at it more though. I don't like to give Ace to shelties, but I'm just funny about that...praying for a speedy, uneventful recovery