For example, sometimes a dog takes a dislike to a person (for whatever reason) they've met once. They might not see this person again for months or years but when they do their behavior towards this person suggests they have some long term recall.
I'm no expert (as evidenced by my newbie posts) when it comes to human OR doggy behavior. I do believe we don't know everything about how their brains work.
Dogs DEFINITELY have long term recall. It varies from dog to dog, but most DO NOT need a huge number of repetitions to learn a new behavior. The trick is to make the CONNECTION between the behavior and the cue. (and, of course, the dog needs to WANT to work for/with you
) It's much harder than one might think to get a new idea across to a being that doesn't share language with you. (try teaching another PERSON something without using any language!!!)
HOWEVER, it's much easier to teach them to DO something than it is to teach them NOT to do something. That's why so many dogs are great with basic commands like sit, down, shake, but their owners are still having trouble with potty training and barking. When you are teaching a dog NOT to do something, you are training away from something that already has intrinsic value for the dog, or they wouldn't be doing it.
The other problem that we have with dogs (and many animals) is that they do not generalize well. You can train them to do a sit-stay in your kitchen, but that knowledge does not immediately carry over into the back yard, let alone a public park. Each time you work an exercise in a new place, you make it easier for the dog to generalize that "we ALWAYS do X when my person says Y"
Same thing with potty training, and why it's important to extend their area of freedom slowly. The puppy first learns "I don't mess my crate (or bed)", that then becomes, "I don't mess my ex-pen", to "I don't mess in the kitchen"...
Many people get caught off-guard when their young dog, who is completely reliable in their house, goes to Grandma's house and has a "mistake". Everyone is shocked! He KNOWS better! Well, not really. It's not HIS house, and he hasn't yet learned that you don't eliminate inside ANY building. THAT takes a LOT longer!
So it's not a memory issue... it's a lack of ability to generalize their knowledge base to new situations.