That is no way enough protection. A female pit bull climbed a section of the three-foot fence at the back of my yard about two months ago. She just had puppies and was looking for food and was friendly. Animal control came and got her, but no sign of the puppies.
Put up a fence that the pit can't climb; a chain-link provides footholds for their paws to use and they are strong enough to use them.
That is why I am going to put up a 6 foot wooden fence to keep the pit out.