Well. Play stupid games, win stupid prizes. Now your org gets to pay for cleanup if they don't just tell the 2 that got arrested "Good luck, you're on your own now"
What's the correlation with Stonehenge and the fossil fuel industry? No one visiting is going to see the vandalism and think "Maybe I should lessen my personal dependence on fossil fuels.", they're just going to hear how it was this asshole group that happens to be named 'Just Stop Oil'. I highly doubt that's changing anyone's mind (for the better).
Don't get me wrong, I'm all for activism. Hell, I'm all for destructive activism; Block access to oil wells, sabotage infrastructure (preferably in a way that doesn't cause more environmental damage in the process), burn down some private jets. But don't go around being an asshole unrelated to your cause just to get your name out. That's not helping anything.