I prefer not to have feeder pens. If you have a hog problem then just start some population control. I find that most deer will not go in to a pen. On our lease we have about 1/2 the feeders with pens and half without. At the ones with pens there seems to be one deer, normally a young buck, that goes in to the pen.
I find all kinds of deer, bucks, does, young and old in my feed pen and when the feeder goes off, they make no bones about jumping in. Population control on the hogs is necessary, but impossible to do in some situations, so you better have another way of keeping them at bay.