Also have you given thought to how you prove you randomly distribute the mines? I assume you will need a client seed of some form. It appears that by non-random placement of mines, you can generate solutions that average significantly more difficult than random mine distribution, so to be provably fair you need to give users a way of controlling the shuffle.
We have a special page that explains the proof step-by-step for each game played. An overview of how it works: There's a client seed, which is mixed in with a server seed.
The game shows you a hash of that server seed before starting each game, so it’s not
possible to manipulate the game board for either the player or for us. We use the seeds
as inputs for the random placement of mines. There is no bias in the placement of mines.
For the nitty gritty details, see: https://www.bitcoinminesweeper.com/provably-fair
