I don't think that you ever 'rid' yourself of lilly beetle. Just keep picking them off and squashing them.

You are more likely to see the adult beetle at certain times of day, like when it is sunny and warm. As Bulbaholic says, it shouldn't be that difficult to control them if you check the plants regularly and crush every one you see. They are harmless so just use your thumb and forefinger.
If you've tried to control asparagus beetle in the same way, not to mention colorado beetles on potatoes, then you'll find lily beetles a doddle.