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I would never tie it on takes so much time.

This video is good to show a way to make the veg stay put, how 'veg' in this case dead stuff effectively camouflages your shape, and also why elastic is >>>> dental floss.

Skip to about 7:30 to see him vegging it up.

You can put elastic (as WorstInFinlanD says hair bands are good, alternatives are simply elastic bands or coloured elastic stricks) on you ghillie, on webbing/camelbak.

Something permanent to attach foliage to will save time in the long run.

You can also just stuff more veg in as it starts to wilt during the day, or when you move area. Can't do that (without taking it off) with a tie on method.

 

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Looks good but that guy didn't put any burlap on his ghillie at all, he's just relying on veggies. It might be sort of hard to fish out the elastic underneath all of that burlap.

Might be but its not. That's precisely what I do!

Not the best photos in the world but here you go.

First is no veg at all (its lying on the ground, without me in it just under the branch at 45 degrees):

Next part filled with veg:

Then a distance shot propped up one some sticks:

Finally a close up from exactly the same camera position: