Thanks everybody for the congrats - much appreciated. I didn't unearth the map myself, I have a friend who lives much closer to the spot, so they kindly agreed to dig it up. I decided that time was probably of the essence given the rate of discussion on the BB! The map itself is of the old parchment type (I have a pic via phone), but it's not immediately obviously how it will be 'solved' - at least the time pressure's off now!
My hope was that we would be able to work it out in time to go and unearth the hare over the weekend, but we'll have to see how that pans out.
As regards the solution to this point, I can at least confirm that the correct phonetic message is:
OUR MAP LIE BENEATH THE MARK WROTE IN STONES
I am happy to post the rest of the solution if that's what most people want, but I don't want to ruin it for anyone who would prefer to work with this message for a while, in the knowledge that it's correct. I'll go with the concensus of opinion.