How to hold houses down

My pigs are really into the house moving business.

The houses that I bought for them have a side hole and both of them (boar) will stick part of their head in, lift the house up and subsequently moving around. This is normally what I find every morning, that the houses have moved.

Since my pigs does most of their businesses in their own houses, I would soon see a path of their migration? Anybody had this before?

My boys also love to rearrange their homestead. They move their pigloo and their tubes all over the place. I think it is just their way of adding their own personal touch to the place like anyone of us would do to our homes. Is it really that bad that they move their house?

I have seen both of my boars knock their heads against the doors and windows of their houses but they are unable to actually move them (they are large wooden type hidey houses). Though during floor time (when I use the Pigloos) they move those all over the place. They also move the tubes around in their cages.

Our large boars, which are only about 10 months old flip over their igloos all the time, so we put small pieces of brick on top of the igloos to weight them down, so when the boar throws his head up... the igloo won't flip over!
The rest of the cage decorations pretty much stay in one place for me.
Christopher