Put a fence/rope/boundary around the land with a notice that is is yours
and
date it.

Our old neighbours back in Nottingham did that with half an acre of land
behind their bungalow. It was unused for many years and there was no
apparent owner. I'm not sure of the technicalities involved but after a
number of years they were able to stake a claim on it and have it registered
as theirs. Potentially it is worth a fortune now if planning permissions
were granted on it. Since it is already surrounded on all sides by houses
anyway and in a residential area the only problem would be access, but with
the demolition of a couple of properties there would be room for a modest
housing development, particularly at today's high densities where everyone
stares out of their windows straight back into someone else's - one of the
reasons we moved to France - no "neighbours" and an acre of garden :-)
--
David
.... Email address on website http://www.avisoft.co.uk
.... Blog at http://dlts-french-adventures.blogspot.com/