Some of these ideas might be good, some might be bad, some might apply to you, some might not. Your mileage may vary.
Adding 'RFONLY' to the end of your path should result in Igates not passing your beacon to the internet.
Caution: You should be really sure you want to do this, because it can lead to the usefulness of APRS being diminshed if you totally remove your beacons from the internet system.
This could be useful if you are able to send beacons at two different rates, you could send beacons for local use using WIDE3-3,RFONLY at a faster rate than beacons designed to keep distant users informed with a path of WIDE3-3 for example. This would give the local users rapidly updated information without cluttering distant networks with less relevant beacons.
Igate Tx Power
If you are Igating national APRS beacons to RF, it might be a good idea to reduce your transmitter power to that which will only just be reliably heard by your nearest major digi. This might help the local users to get into the digi without trying to compete with your powerful signal. It is more important for local users to get into the RF network than for distant ones.
Of course using a lower aerial will achieve the same effect.