The following image is an example of a typical cairn protection setup. There's a palisade, a landclaim and a hearthfire inside the palisade which you can't see.

The landclaim is to make it harder for the opponent to build a palisade around the main palisade. It also prevents the pali from decaying.
The hearthfire is so the cairn's owners can monitor for wrecking balls. A naked alt is enough to take one down, even if the opponent has a warrior parked nearby. If one naked alt isn't enough, they'll send out several so that while the warrior is busy knocking one out the others will take care of the WB. Keep in mind that having a warrior sitting by the ball all day is hard enough to begin with-- who wants to waste their entire day for this when their efforts could be foiled by a bunch of naked alts?
The main palisade will take 24 hours to bash with a wrecking ball. That wouldn't be a big problem if multiple cairns weren't protected like this and if cairns weren't so easy to replace.
Thoughts?