constantly. Another one didn't have good obedience training and always jumped up on everyone and couldn't refrain from being a nuisance. The last one was owned by a deaf family; it alerted them to visitors, etc., and was well-behaved.
They're just so big and energetic that they're one of those breeds that should only be owned by highly-involved owners that know what they're doing. If they aren't properly trained and cared for they become real problem animals.