Yep. The shock collar was a very, vary bad idea. You have ingrained the behavior on the dog. You will need an animal behaviorist to help you here. To over come this will take patience and much work. I suspect we are dealing with a fear aggression, even though you don't see signs of fear. Many dogs don't exhibit what humans would detect as signs of fear. They show their fear in other ways that a trained professional would pick up on. You have used exactly the worst method to solve this problem. I don't mean to make you feel bad, but anyone who reads this needs to know for themselves for the future. Never, ever use a shock collar for outbursts such as this.

In fact, all of the things you've mentioned are horrible for this behavior. Pennies in a can, water bottle - all are punishments. This behavior needed exactly the opposite. You needed to do what is called "Classical Conditioning." Well, actually you did Condition, but instead of conditioning your dog to a positive response, you've conditioned your dog to a negative response. YIKES!

But, this can be helped to some degree, even at the dogs advanced age. What you will need to do is get an animal behaviorist to come and show you the steps. I wouldn't seek help over the internet or in books. (I think you've already done that, and this is the result). You need in person, one-on-one help by an "all positive" trainer or behaviorst. "All positive" is very important.

Good luck.