For those using FL studio, I recently made a Patcher preset that makes it impossible to phase out a watermark by making inaudible (very small) random changes to the pitch.
Just put it in the channel your watermark is and it works automatically.
I used Patcher, Formula Controller and Pitcher.
Link to preset: http://www.mediafire.com/file/hltp4q89co3ec29/Anti_Phase_Inversion_(AJ).fst
Drop it in Image-Line\FL Studio 12\Data\Patches\Plugin presets\Effects\Patcher