As far as cattle go, I don't believe longhorn cattle are any worse on fences than other breeds of cattle. As far as objects in the pasture, I would protect them as well as possible, regardless of the type of livestock you are running. I guess it just depends on the individual animal, but some of them just don't seem to respect fences or anything else, whereas others seem to stay confined pretty easy.
For example, I have 1 horse and 1 pony on the 6 acre pasture around my house. On the 100+ acres behind the house, we have 3 horses, currently running with the cows, but soon to be seperated off to themselves. So far, this situation has worked pretty good. Anyway, the other day my neighbor calls and says his horses have escaped his temporary fence around his 2 acre place, and he asks if and can leave them at my house for awhile. I told him, sure no problem. So he brings them over and we turn them out on the 6 acres. As we were turning them loose, I asked him if they knew what a cattle guard was, and he said he wasn't sure. Well, about 5 minutes later, the 1st horse was walking right across the cattle guard and down the county road, and then the 2nd followed right behind. Neither horse was hurt, but it was a little tense at one point.
Needless to say, I gotta open and shut the gate till he gets them back to his place.