While I respect Jackdale and Faster's opinions, in this case I disagree with their objections to the use of a boom vang as a preventer. This use for smaller boats is mentioned on the UK-Halsey sailmaker's Encyclopedia of Sails website page for boom vangs: SKIPPERS TIPS ON USING BOOM VANG - UK-Halsey Sails
I have done it a number of times with no problem. If you secure the boom vang to the rail and tighthen the main sheet and the boom vang the boom will not be going anywhere - it cannot generate any power to pull the stanchion or rail fitting. The boom will be held in place by two forces down from either side. The power from a jibe is generated by the speed of the movement of the boom, not the power of the wind on the sail from a stationary boom. If the wind moves forward of the leeward side of the mainsail, the boat will simply spin into the wind; there is no particular movement of the boom, particularly if you have also positioned the traveller to leeward, as it should be.