I rest a wooden spoon, handle side down, into the neck of the flask, that helps deter boil overs.
I also use a spray bottle filled with water, which is far and away the best boil over tool at your disposal.
Kegged and serving - American Wheat, Daves Porter, Outkast Kolsch, Nectar of Nuggets
Bottled: French Canadian Breakfast Stout, Edworts Apfelwein, Westminster Wit, Put that in your stout and smoke it
Fermenting: Apfelwein, Flanders Red, Skeeter Pee, Heady Topper attempt #1, Kumquat Berliner Weiss, Sabraton Accident Stout, Nelson RyePA
Upcoming: Session IPA, Yeti eqsue stout, Dark English Mild, ESB, CDA, Row 2 Hill 56, Zombiedust, Hoppy Amber, Geuze, 100% Brett Golden Ale