^^^This. This thread is about someone asking for help, not a "I know dogs best" thread.

It is very rare that a dog is just a random biter.
Generally it is a reaction to a fear or aggression of some type.
99% of the time there are also warning signs.
Yes there are the 1% that randomly bite with no warning signs.

I would ask how old the dog is?
Why type of training has it had?
How much socialization did you do with the dog as a pup?
How much time is spent walking the dog on a lead?
What breed of dog is it?

Not necessarily , time limit or number of dogs owned does not make you understand canine behaviour.

I would have thought after 40 yrs plus, you would have learnt that dogs dont just bite for NO reason, there is always a reason, its down to you to find that out, before you act on it.

If I remember correctly you had your dog PTS without hesitation when it bite you, finding out after the event it had a brain tumor............ so there was your reason for your dog biting you, it did not do it for no reason,yet it paid the price because you did not take the time to find out the problem.

Something that is ALWAYS advised here when people are having problems is to have the dog health checked , as often there is a underlined reason why the dogs behaviour has changed........

Ask a commercial kennel owner you say ?
They might say there is no reason but in truth a dog has been taken away/ abandoned and are all alone trapped in a cage, then strange possibly untrustworthy people come in and out, that alone would be more than enough reason to trigger a fearful dog to bite

http://leerburg.com/aggresiv.htm

This article may be helpful.