Tough to even try this or practice where I play. Before you finish one rack, a group of 3 or 4 watchers will gather and begin to talk loudly about politics, boating or the weather and they never shut up. These are the guys that will take their lawnmower to the repair shop when it won't start because the gas tank is empty. All this talk is within 3 feet of the table. A couple will even do commentary on each shot in the rack. Being nice to them doesn't help. Being rude and vulgar to them doesn't help either. If I chase them away, it won't be 5 minutes before 3 or 4 more come over to do the same thing. It's supposed to be a poolroom, not a day care center for elderly men.
Heads Phones. Use head Phones, works really well for me.