Ok, this is a long reply, and I may get cut off in the middle, so check back for more...
I have a friend who was in on the beginning of the organic farming movement. In his words, hogs are much better than chickens (in a tractor) because they really turn of the soil.
Now, turning up the soil is great for where you are going to build a garden.
It is awful in areas where you wanted to be left as grass. They really destroy the grass, and so your other grass eating animals will have nothing left for them next year.
A male hog will easily lift those timbers and get out whenever he wanted to.
The female hogs... it depends on their disposition. But each of those hogs in the pictures, their snouts are as strong as your hands are.
So, to reiterate: If you are putting the hogs in a place where you are going to build a garden, great.
If not, you are just tearing up your soil and it will get washed away in the rain.
Your cage isn't good enough to keep the hogs in if they decide they want to get out.
Hogs need more area... well, during the hot months they need an area to take a mud bath. Other times of the year they need an area to take a dust bath. They also need a shed type structure for the winters, and a shade area for the summers. They also need a pen that is more than 4x4s. As in welded pipe, or 6x6 posts.
So, I suggest you start looking into a proper pen for your hogs.
A packed earth lean-to is something you may want to look at.
A male hogs snout is stronger than you are at lifting. If they weren't such pigs, we could probably train them to be fork lifts. ^_^
From my experience with hogs (about 800 pounds of famished pig), I must agree with you. I have seen a hog bust through a 2"x12" without much trouble. They are also great at destroying bramble patches, and taste better for the blackberries they eat when they do.
I'm sure they'll love the fresh grass, but I am also quite certain that if they decide to exit the structure, what I saw won't hold them back much.
Yeah, these ones really like a good mud bath. They took their previous more permanent pen down to the bare dirt without much effort. I'll be covering it with mulch and beginning to build the soil for a no-till garden there.
Thanks for the advice.