At 30' deep,you can't put screw types anchors you will have to go with weights.
Concrete looses about 35 % ( ? ) of the weight in water but...dirt cheap!
If no current,dropping anchors through the ice could be done and easy to survey.You will have to reajust subs and bouys as the water fluctuates or have to add some systems if you want them to self adjust.
More things to break and fix on a public lake,not a good thing,you want to ski more then repair.
Good luck!