Stanwell,
Have a read of the link I posted and view the video at the bottom. This was a "test" done with on an actual canopy. While the little plastic hammers are sold for cars with toughened glass they do pretty well on the perspex given repeated efforts. The trick is that once a crack is formed you have to work it along bu hitting again ahead of it. The spring loaded breaker thing didn't do too well.
no_one