In a broad sense a behaviour problem could be any dog behaviour that is problematic for you or your dog.
Dogs have many natural behaviours that are problematic for humans such as barking, jumping, digging, biting or urinating where they shouldn't. These problems can usually be solved with training and enrichment.
Normal dog behaviour that starts out as a mere nuisance for humans can develop into a more serious problem behaviour for both dog and human if it is not properly identified and modified.
It is always better to address potential problems early than to wait until either you or your dog become seriously stressed.
Go to the Dog Training section to learn more.
If your dog seems anxious, behaves fearfully or aggressive, injures others or themselves, has compulsive behaviours, barks excessively or is seriously destructive, or if their behaviour changes all of a sudden, it's time to get help for you and your dog.
Whenever you suspect that your dog may have a psychological or medical problem, consult with a suitably qualified professional.
Talk to your vet if your dog's behaviour changes suddenly. There may be health issues that need to be addressed. Pain, discomfort or other problems can affect a dog's behaviour significantly.
If your dog is physically healthy but their behaviour concerns you, talk to a qualified dog trainer or behaviourist*. A solution may be straight forward or it may involve several measures. Some problems are solved by management alone, others involve management plus a behaviour modification program.
Talk to an expert so you can make an informed decision.
* Note that a good dog trainer will always refer to a specialist if required.