best way is to say to league A i'm free the first and third saturday, the other league the second and fourth. that way you know where you stand.
If league a dont have a game for you on the first or third, then you can go back to league B and "open" a date you had closed.
If you leave both leagues open for the same day, and they email you with and hour of each other, but you dont check your emails for 3 hours, you've got to tell one that you are closing a date, after they have assigned you a game = bad reputation for dropping out.
As for the county - if you close a date with the county, you can not do ANY games for ANYONE as County takes priority.
ie You have 18th open to League A, but closed to League B.
League A says you dont have a game on 18th; you contact league B and say "im opening up 18th as im free if you need me."
League B give you a gave - hunky dory.
Then on Thursday the County give you a game on 18th - you accept the county game, forward the appointment to League B apologising that you have to drop their game as CFA have given you a Game.
What you can NOT do is tell the COunty - thanks but no thanks, I;ve got a League game. well you can, but lets call it refereeing suicide.
But if you have the 18th closed with the COUNTY, you MUST have it closed with the leagues.
Best way is get a calender / wall planner / diary and put three lines / columns = County at the top, League A and League B.
If you cross out and close a COUNTY, then close the other 2 also, and or alternate you other leagues.
Generally County will be for cup games, which will be sproadic between Aug and Jan, then as they move throught to QF, SF an F in MArch, April and May. YOu;ll get an idea if you are getting / earnt any of these.
Think i've had 3 County cup games per season, but County also have to assing assistants to the PL U16, U18 and U21, if that floats your boat (think LFA, Everton youth teams etc)