Thanks, Walk Tall, for the advice.  I must admit that when I first went haring off to find one I expected to see something fairly big, I don't mean huge but detectable    I have a friend who lives abroad and he is a keen geo-cacher so I sent him an email, when he sent the reply and explained the size of the thing I was looking for I laughed to myself.  Admittedly I did find those.  It is just trial and error isn't it.  At least it gets me out walking, although not in this heat.

Thanks, Bear and Ragged, I will try to keep it going even though there might not be much to say.