"to use a compass accurately you need to be away from the bicycle. bring a silva."

May be true, though the same issue pertains to boats, aircraft, and there is a process for dealing with it called swinging the compass. Whether this works with bikes I can't say, you sure couldn't be moving you metal stuff around, if you have it. Just something like turning your fork might make the readings go nuts... Does seem like a case for a handlebar mounted GPS if you are prone to getting lost.