If you have claimed territory normally you can't place a new claim flag within a certain distance of your existing claim. However, you can do the following:
1. Have an ally contest your claim by placing a flag close to yours.
2. Then contest your ally's flag by placing your new flag a short distance from the ally's flag.
3. Lastly, have the ally remove their claim flag. Your new flag is now uncontested and it will complete at a shorter distance to your original flag than is normally allowed.
By repeating this method you can spam claim flags in much greater density and thereby increase the time required for an assailant to capture your territory many fold.