Paint your wall top with that black sticky gunk they use to keep pigeons
off
ledges.
Or, one better, put fake bird muck on the top of the wall - you could
probably make some fake stuff (anyone got any recipes?)
Au Res.,
Paul
--
http://www.efbenson.co.uk/
http://www.users.waitrose.com/~paulbines
http://www.convergent-diversity.co.uk/