Lines under the ice in these backyard rinks are from lights. You can also use a vinyl sheet and freeze it inside the ice. We prefer to use lights to add lines and markings to our rinks because they don't attract sun during the day which melts the ice in those sections quicker. You can also use bingo dabbers to create temporary lines. They will come off as you skate, but you can re-make them as many times as you like. The kids love drawing on the ice with them too.