Have you tried a longer E collar?
They can remove their stitches- hopefully it will hold this time.. I know this sounds stupid but it worked for me once- I took gauze and wrapped- get this- one back foot.. lol.. The dog would spend time trying to get the gauze off- and of course leave the rest alone.
Seriously though- sometimes the E collar is not long enough to prevent them from getting at the stiches. The dog should be able to drink, but the sides should be longer..