one of the hardest muscles to hit, imho. they normally get trained when doing pulling exercises. or on the negatives of pushing exercises, yun nga lang may risk sa joint when going heavy.
saw a variation of lying rear delt raise from youtube, incorporated it into my program, and got DOMS the following day. i don't have the link to the vid anymore, but i did save it in my home PC. try ko post link pag nahanap ko ulet youtube vid.
bale higa sideways sa bench hindi sa ground, tapos kuha ng plate na mababa timbang, parang rear delt raise din ung arm mo - parallel to the ground @ sa head, so baba mo yung arm mo sa ground, tapos raise mo ulet - pero instead of raising it fully to the air, hanggang doon lang sa shoulder height. tapos go to failure. then next weight ulet. did it only for 2 sets and wow ramdam.
so how do you target yours?
edit: found the youtube link IFBB Pro Chris Cook teaches rear deltoid technique -> www.youtube.com/watch?v=7CGp-HUz5uI