Advice to New Adopters for Dogs Missing Their Foster Mom?

I am fostering a great little dog that has lived his entire 1 1/2 years in an outside kennel at a so-called rescue facility with many other dogs. I'm probably the first and only human that he has been closely exposed to. He has become very attached to me and goes bonkers whenever I come home or pick him up from groomers or daycare. Its funny because he never does this when I leave...just on my return. Does anyone have any advice on how I should advise any prospective adopters on how to deal with this? He was adopted out once but returned because he kept digging out. He never does that here and he is the perfect little gentleman.