"Walking Tall" - the original with Jo Don Baker....great story

Sounds like his jealousy of the new dog and fear of being abandoned again is causing him to make sure everyone knows this is his territory, so he's marking it...

My guess is that it's there for a reason. Probably best to leave it alone and not try to go around it....

Probably not, but some chemicals in products we use, especially medications acnb change their chemical makeup and become dangerous, possibly poisonous. It's a good idea not to use any product beyond it's expiration date...

No people should not end their lives. Why? Because God says it's a sin...

Depends on how many tablets your dog ingested and the size of your dog, but  In animals with vitamin D toxicity watch for vomiting, diarrhea, anorexia, excessive drinking and urination, depression, hemorrhage (bleeding), abnormal heart rhythms, bone pain and limping. If any of these are present immediate take your dog to an Emergency Vet Clinic