This brooch by #lizziwildeevans could have magnets at the back.   You embed one or more 'sacrificed ‘ magnets into the back of your piece when curing, then take it out and put in a new magnet (one of these, or one of these – or both)  This because curing takes away a lot of the strength of these very powerful magnets.   You then stick the magnets with quality glue  and use further magnets to hold the piece in place on the inside of the garment you wish to use – thus saving the fabric from damage by pins.     

Important: those with pacemakers should not use this method