Glad to hear the surgery apparently got the nasty cells out.

If leaving for a few hours, I give mine rawhide chips to munch on. Usually their stomachs over rule their separation anxieties. For the most part all I have to say is "pen-pen" to mine, and they run into their pen- waiting for their treats.

You could try something similar to car training for the separation anxiety. Pretend that you are leaving. Exit out of the house for 20 seconds and then come back in and let puppy out of the kennel. Repeat a couple times a day. Then extend the length of departure to 1 min, 5 mins etc. If nothing else you get to visit the neighbors a lot.