Right now you can make a basket on someone elses land. You can set permissions for it but you can not pick it up. If it's set to "private" then you can block land of other people which is effective way of griefing tribes. And no one can clean it up if permission stays on private.
Another way of griefing with this tech is by making few baskets next to someone elses baskets (when he is not looking) and set permission to public. Once you have done that someone from that tribe just might start puting stuff into the basket and you can sneak up and take it without any problem.
I short = xploit material. Please don't allow anyone but tribe members to make and place baskets on the ground of that tribe. Neutral or shared baskets should never be placed by outsiders.