Help for autistic child "danger" awareness?

Well I will certainly go and read that, I have 3 children myself and one is a very hiper little boy and does not know the word danger. I am always outside with my children my oldest is 12 and she hates it, but she understand my youngest is also 8yrs old, and teachers have a hard time with him in school having to keep him sitting down, but what I do with my younger boy is that when were out and about now this may sound rude and stupid, but my mom told me she had to do this with my brother and he learned, but its like a dog leash ok, it goes around your child like a harness, and you attach a cord to it, again may sound rude and stupid and its not a pet, but my son learnt that he could only go so far from me, and when I saw something dangerouse I give him a little tug and he would fall back on his bum, now he is 8yrs old and when he sees certain things he remembers falling on his bum that hurt and is starting to realize if he goes near something or tries to touch something he thinks about his bum and how it hurt, its getting better each and everyday, but I know some ppl would say I am not doing that, and I say do not kick it unless you have tried it, and besides you asked for advice, so here is mine.