How about using one of the UltraLite antennas by K1JEK and bending the ends to fit your yard? For bending info, see
http://www.comportco.com/~w5alt/antennas/notes/ant-notes.php?pg=16. For UltraLite antenna info, see
http://www.k1jek.com/. I use the UltraLite Sr. in an inverted V configuration with a bend of about 14 feet from each end to fit the antenna into my yard.
73, Chuck