I like this version a lot, HB. There's more energy in this beginning, and I like the dialogue better, I think. I agree that it's no problem you're showing them fail, at the start. There's drama in failure, and they're trying, which is more than a lot of people ever do.
Maybe that's part of the answer to your post just above. I'd feel it perhaps a bit too much, and a bit unlikely, if, in the first few pages and in the midst of their highly stressful act of vandalism, there was too much backstory given as to why they were there doing what they were doing. The kids would understand why they were there, and telling us would just seem like 'telling'; the deeper motivations for their actions can come later. They're trying, which maybe is enough to show, at the start.
I would think that the action of sidelining a few pieces of heavy construction equipment would seem sufficient enough result for kids new to aggressive disobedience. Could it be mentioned in an aside that if this is successful, it may be just the first act of a planned series of acts, toward their goal of saving Doaky? I also like the thought of the spray cans...the kids could verbally practice the various anti-establishment tags they might leave on the equipment or buildings, with Rick going for a goofy, funny one (perhaps this could be before they start cutting the fencing, when the newbs are too nervous to actually start, and are delaying the point of no return by gabbling on about slogans). I thought, BTW, that Rick's line of dialogue that ended the excerpt was very funny. It was a great place to cut the piece.
Final thought about this: 'The gunshot wire-snap...'. I like this, but just another option...I've heard laser pistol/rifle firing-sounds from movies or TV shows that sound sort of like the noise a piece of taut wire makes when it's cut. Anyway, a good start, IMO. Best of luck with the book, CC