Put twist ties at the end of the bags. you want to leave about an inch of space between the opening of the bag and where you place the twist tie. BUT you also want to have some space between the icing and the twist tie, that way when they grab the bag to pipe, the icing has somewhere to go when they squeeze (and it wont come out of the top). I hope that made sense! And I hope thats the answer you were looking for!