dog play dates

Question
I have been setting up play dates for my 3yr old dog( Australian shepherd Russian wolfhound mix) with a 1 1/2 yr old (terrier mix). My dog LOVES this terrier!!!

We are trying to establish play dates so that our dogs can be more engaged while we are at work. I have been stepping in to leaving them on their own gradually. But what I have noticed that causes me concern is that my dog cannot say NO to the puppy play. She has played non-stop for nearly 4 hours at a time!!! I have had to intervene and separate them. Normally my dog would sleep most of the day if left on her own.
  I came home from work this morning to check on the dogs, after leaving them on their own for 3 hours, and realized the 3 hrs had been once again non-stop play. My dogs heart was pounding and she was breathing hard. The terrier doesn't seem to be labored by this play.I took the terrier home.

I was hoping that she would adjust to the terrier and relax more. The terrier will only keep playing when her invitation is accepted.( she is submissive that way) My dog doesn't seem to know when to say NO to this dog. ( PS. My dog doesn't play much with other dogs...just once in awhile something clicks).

Now I am worried this will be too much for my dog. And interesting that so far I am told when at the other dog's house, my dog just lays down and barely plays!!

Any insights on how to proceed? Or is an all day visit just to reckless for her. I am afraid she will have heart failure!!!

Answer
Dogs sleep when left alone, and even when not left alone (dogs sleep a lot.)  Your dog appears to be on this non-stop play behavior BECAUSE she is in her own space.  This may be a proprietary behavior (maintaining control in her own space despite her exhaustion).  Play is NOT "play" in the sense humans experience it (as children.)  Play is a rank behavior, meaning it shapes adult pack behavior.  Your dog may be totally unable to refrain from engaging the other dog due to the fact that she is in her own environment; clearly (as you state) when in the other dog's environment, she refuses to play, or plays sporadically, which may mean she is VERY aware of environment and will not demonstrate any dominant behavior in the other dog's space.  Continuous interaction in play is, I repeat, a rank behavior; if your dog persists in her own environment, but desists in the other dog's environment, she is acquiescing to rank.

It is never a good idea to physically push any dog beyond its limits.  The Borzoi (Russian Wolfhound) has a deep chest and is a high candidate for gastrointestinal obstruction (stomach flips over) which is deadly; high blood pressure related problems (which can develop into heart failure) and a known candidate for congenital structural heart problems.  The Australian Shepherd is a "control" freak.  If your dog is TRULY the combination of these two (which I doubt, most mixed breed dogs are inadequately identified by most shelters and rescue workers; the Borzoi is a highly guarded breed and it's not likely this dog is a mix of same, although of course anything can ,, and does ,, happen) she is driven by incongruent genetic drives.

While your heart is in the right place by attempting to allow your beloved dog companion to her interact with her "best friend", I suggest that this may be far too much physical stimulus for her.  Dogs do not need daily play dates.  Two to three times a week for short intervals is adequate.  Try to find neutral territory for these two to interact for an hour or so two to three times a week.  You can also meet the other dog's owner for an on-leash walk, side by side, for twenty minutes or so twice weekly.  If something were to happen between these two dogs while you are absent from your home, YOU would be responsible (legally and financially.)  Additionally, bring this problem to the attention of your veterinarian asap.  Your dog should be evaluated for possible cardiological problems (murmur) and an ultrasound of her heart couldn't hurt.