thanks fellas for the respons
as for the sandbags; just the usual methode : roll a piece of airdrying childsclay (brand daz i used) into a sigaar and cutt it in segments the size of the bag, take a palet or knive and press it around the bags to give your stitching, take a piece of medical gauze and press it aroud the bag for inprint , when placing or stacking in position( stil wet) i'll brush some white glue on the underside of each bag (in the past i just place them without glue and when they dryed they just fell apart
)
for the barbed wire :
http://www.finescale.com/fsm/community/forum/topic.asp?TOPIC_ID=34218