I have a possible solution against bots.
Since they can make at least theoretically 24 claims in 24 hours the accounts using that means can be easily spotted and in consequence banned.
It's imposibile for a human being to make free rolls exactly after 1 hour constantly.
not exactly true, my mother and i had a system base on our working hours,
at nights i rolled for myself on my notebook and for her on her smartphone and vice versa at day time, that way we could take almost full 24h advantage of reward bonus + btc bonus..., and still be human rollers ;P
but, a solution based on that concept is still open, simply limit a user to have a max of 12 or 16 rolls day, obviously some other things need to be accordingly adjusted...