Note the ball on the end of the chains on the "necklace" - these are needed to provide enough resistance to trip the fuse, I think?. Modern HEAT fuses are designed to not trigger on twigs and other foliage - the ball on the chain end will likely make the thing think the impact is more substantial than some piece of incidental shrubbery.
As to chicken-wire RPG fences, these stopped the rounds by trapping them in the gaps (there was not that much forward velocity) without triggering the fuse, and also by shorting the fuse if it touched the wires as well (early RPG used a crush pezio-electric fuse). Or it could also trigger the fuse - hence the need for the chicken wire to be some distance from the protected vehicle. All if I remember correctly - the details were in the old 1976 Jane's Infantry weapons section on the RPG, but I foolishly sold that off at a second-hand book shop back in 95 or so. Exellent reference work - but nowadays fiendishly expensive
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Anyway - the early RPG's simple pezio electrical fuse was a weakness and there was a proposed "electrical" defence which generated a field to set these things off at a certain distance from a field generator. It was just a bit big to cart around (so would only have been good for static observation posts etc), and a simple change in fuse design would have made the thing obsolete. Later RPG fuses tend to be more sophisticated.
Oh - and another way to defend against RPGs was to fight on a windy day - the thing tended to "weathercock" at longer ranges as the wind acted on the extended stabilising vanes at the rear end of the round, and so it would end up flying more sideways than end-on..
Cheers
Andy