I don't know if normal defenders have some sort of means to hold the back door open, but mine doesn't and when i decided to hang a spare wheel from the back door, it closing on me became less funny. i say its a problem but its been like that for a year or too now so it obviously isn't too much of a problem.
aaaanyway, the idea of using a gas strut on the back door has been discussed here a bit. i'm not sure if anyone got round to doing it, but after a trip to the scrappies, a friend gave me his two old tailgate struts from a pug 205, so i decided to actually make some sort of stay.
i wasn't really sure if it would work or not so i didn't take any 'in progress' pics. i was somewhat fearful that the rear door would be fired open on any unsuspecting person who opened it or would have no effect at all. anyway there's not much to it, i welded up a bracket at one end and welded some mounts to the existing stay which stop the door opening too wide. my door panel is ply so some fat self tappers were all that was required to attach it. might be more difficult r need more alignment to hit the frame if you have a standard card.
some gas-strut-ish information, if you intend doing this. most gas struts seem to operate on little ball knuckles. on the peugeot these were welded to the body so i drilled out the sockets on the struts and made them into pins. unfortunately this weakends the plastic ends and i had to file mine way down as i had to squeeze the old door stay back through the card with its new mounts on. i therefore managed to snap one end and then threw the strut around the garage sursing and swearing.
fear not though, a look around the family fleet revealed volkswagens have threaded knuckle things, so if you are visiting the scrappy, some of these might do. i think freelanders also have threaded ones on the back door strut. i had gone far enough so i just made do with my now eyed struts, but if i were doing it again i'd go down the vdub route.
the struts dont seem to have any markings on them in terms of strength. all i can say is that the pug 205 one worked perfectly to my surprise and closing is not too much added effort yet it now holds open and can, with a bit of assitance to half way, open 'automatically' as descirbed in some car brochures.
here's the pics, hope they might be of use to someone thinking about it.