I've been there!!
Max was neutered last month and he did everything he could to get to those stitches. He even pulled one out
The onsie didnt work, he ate that off. Sooooo I used Missy's panties from when she was in heat. They were about $20 at PetSmart but worked wonders! They are like a diaper and they are made of jean material with a pad inside, they secure closed with velcro.
After Max bit of that one stich and licked it so much it looked pretty bad. I was upset like you are, thankfully the undies worked! He kept them on for about 3-4 weeks. I would check his stitches daily and remove the undies to wash every so many days but other than that they stayed on all day and night.
I'll try to post a pic of Missy when she was wearing them.