Ok, hopefully by now you've tried the game, and can shoot a respectable round of 18 holes, (some where between 90 which is considered bogie golf and 72 par for 18 holes).
Now you want a little more challenge! Here's what I came up with, everything remains the same except for the following rules. First you MUST shoot at the Bull's-eyes on all par threes on whatever course you play or create, there is no option. Second the scoring on the Bull's-eyes changes to double bull is a birdie (-1) single bull is a par 0 (even) outside the Bull's-eye ring inside the triple is a bogie (-1) outside the triple and inside the double ring becomes a double bogie (+2). Anything else is a triple bogie, (off the board or hit a wire). These rules should be applied to players of A and B level (or above) at this time I should say when leagues are formed they can be formed on each level (amateur and semi-pro) and then simply use the same basic procedure that is used in real golf to create the handy cap system.
The way this is done, is you shoot, and keep track of your first 20 rounds (20 - 18 hole rounds) then you take the 10 lowest rounds and add them together and divide them by 10. This will give you an average that will show where you stand compared to par of 72. For example if your average is 84 then you would have a 12 handy cap. (this is where I started) If you averaged a 76 you then would be a 4 handicap, and just like real golf if you're a scratch golfer (par or less) the same rules would apply.
This would be one way to handicap players shooting the same level. You could just use different levels (and rules) or play between amateur and semi-pro to handicap the better players, but I haven't researched that option enough to qualify it as a reliable solution.