I use Bonide Bon-Neem against the lily beetles.  It is a combination of Pyrethrin and neem oil…both strong contact killers.  There is no safe spray that will get rid of them forever.  You’ll need to start spraying when you see the first sign of them and then every few days.  It is important to kill the first ones as soon as you notice since they give off a scent that attracts more to the area.  They will eventually subside as their breeding season ends.