User blog comment:Frodo the 9 fingered/A Third Camp?/@comment-5112532-20120731101113/@comment-3146930-20120809034818

But keep in mind that demigods/legacies at Camp Jupiter are raised at a young age for survival, as Lupa trains them before they even make it to Camp Jupiter. Meaning that any member of the Roman Legion that leaves Camp Jupiter would already have survival training. Not to mention that the gods don't just ignore their children. If their children formed a third camp, they would offer some kind of protection or they would make their own.

Also keep in mind that Hazel said they could move Camp Jupiter in a matter of days if they needed to. Knowing that, there may not be a third camp, but a collection of demigods that constantly move around so they don't attract monsters. This would also negate the need for a camp border like the other two. However, the gods swore to keep the two campers from meeting each other, so any Roman demigod would still be shielded from the Greeks while the Romans may just write off anyone that leaves the camp.