So this is a little last minute, since I just had this idea and the game's being run in the morning. But for my western campaign, I'm going to have the PC's (On horseback), chased by an airship. Considering all they have is pistols and nonlethal magic, they're not going to be able to shoot it down (Probably), but they can make the shooters keep their heads down until they can reach cover, at which point the Airship will land and it's occupants will get out (They're trying to catch the PC's alive). Any advice for running such an encounter besides having the PC's riding hell-for-leather and shooting to keep the sharpshooter's heads down?