Chris, everything you are seeing in Beckon is the norm for dogs who have gone through amp surgery. Most dogs don't pee or poop for 2-3 days post surgery (I misunderstood your first post after he got home and thought he had peed and pooped...which would have been very unusual)...if it goes longer than the 3rd day then sub-Q may help. The other option is to use a syringe and squirt water into his mouth several times a day...this usually works well and saves the stress of a vet trip. The instability is also 100% normal and as the drugs from the surgery wear off (next couple of days)he may also evidence some pain and seem depressed. Be very careful not to stop pain meds too soon...pain is a stress factor and will not help in the healing process. Amp surgery is a huge trauma on the body and the first couple of weeks as you go through these "down" times you may find yourself wondering if you have made the wrong decision. I cried myself to sleep several nights during Sketch's initial post amp weeks when he was going through a tough spot, thinking that I had done something horrible to him and it would have been kinder to let him go. Then about week 3+ things start to get so much better and you will see your beloved Beckon coming back and be thankful you made the choice to have his cancerous leg removed. But right now for the next couple of weeks the absolute most important thing you can do for him is rest, rest, rest.
This is an emotional journey, even more so for you than for Beckon...take good care of yourself too.
Hugs to you and Beckon, Trini