Dog behavior changes

Question
We have an almost 10 year old queensland heeler, border collie lab mix who most recently has become quite clingly to my husband. He is always right next to him, laying by him or just with him in general. He still eats well, and plays like he is a puppy sometimes, doesn't mind our girls palying with him so I'm not sure if he is just getting old or if maybe there is an underlying issue. He seems to be in good health.

Answer
"Seems to be in good health" doesn't work.  Older dogs require full veterinary examination every six months and a complete metabolic profile every year.  Take the dog to the veterinarian and report this change in behavior.  Have a full blood chemistry done, a basic neurological evaluation, an eye check and an orthopedic evaluation.  Also, watch your husband: is he under particular stress of any sort, not feeling well himself, etc., offering any subtle signal to the dog that something is 'wrong'?  Observe what the dog does when your husband is not at home: is it his normal pattern of behavior, or is he actively avoiding people/places, spending more time alone, etc.?  It may be your husband has precipitated this with subtle body signals due to stress at work, unusual fatigue, other normal factors; it may be the dog is feeling more anxious because of pain or some physiological problem and is seeking comfort from the "alpha male" in the household (your husband); it may be the dog is beginning to suffer form some cognitive dysfunction and there is a medication to treat this (Selegiline).  Think about and observe these things before going to the veterinarian so you can present as full a picture as possible.