Hi Gameplayer... I think 10 squares is too much. Elgea is so crowded that having a neighbor 10 squares away is very common. If 5 squares is the norm for claiming rights to rare res, then both players each have some domain to claim their own resources. If you go with 10 squares, then there will be many cases where a resource could appear right next to your neighbor's city, yet still fall within your 10 square claim.
For herbs and minerals, I would respect a 5 square distance from any settlement without prior permission. For animal parts, if I kill it, I will harvest it even if it's closer than 5 squares. But that is a bit different - since I paid for the kill with any lost troops, I think it's fair to harvest the parts regardless of their proximity to any city. Also, once I harvest, I'm gone, so it's not the same as trying to hold something for a long time in an area that is clearly someone else's territory.
Just my opinions, obviously. I know others hold to the 10 square rule. I have already had to battle it out over an herb square that was 5 squares from my city but 6 squares from an alliance who held to the 10 square rule.