Jamieson, Fausset and Brown on 1 Samuel 27:5

5. let them give me a place in some town in the country--It was a prudent arrangement on the part of David; for it would prevent him being an object of jealous suspicion, or of mischievous plots among the Philistines. It would place his followers more beyond the risk of contamination by the idolatries of the court and capital; and it would give him an opportunity of making reprisals on the freebooting tribes that infested the common border of Israel and the Philistines.