Hi Bernie. Dogs will urinate unitentionally like this for many reasons - the two most common ones being submissive urination and excitement urination. They don't mean to, they don't aim to, it's just a reflex action pertaining to their emotions at the time.
Like the urine from a dog who pees submissively smells very different to another dog than the urine from one who has peed from being overly excited.
The more excited Bernie gets, the more the likelihood he will inadvertitently urinate, I'm afraid.
One thing to consider is the fact that a confident dog will rarely urinate when excited. This behaviour (or should I say result) usually happens with dogs who are not overly confident in one way or another. Hope that helps.