My dad says "Hike!" with a hitch-hiking thumb gesture to get people to move out of HIS spots. I have no idea where he picked that up, but now we all say it. One can be quite blunt if one is pleasant and slightly humorous. "Move it or lose it" is another he uses. I think the English expressions must have tickled him when learning the language. Camp etiquette for us -- we have two regular trips a year with the Prof's family -- is to use any chair until its owner claims it, then move, and it is fine to claim it bluntly as above. People are territorial and I have never found claiming one's own to be a problem or require an explanation, nor does anyone think it rude. I might tell a small child we can share, and to sit on my lap or snuggle in next to me once I am settled. We have had Great Chairs appear, everyone loves them, but defers to the owner, asks where they were purchased, and then everyone has them the next time. We do defer to the aged, infirm or pregnant if the Great Chair is significantly better for them, and revert to the older model, barring personal special needs. I have never seen anybody in our group not cheerfully relinquish a chair to its owner, however, special needs or no.