I've a pair of bookshelf speakers of a similar size (Kef iQ60s) for the rears on my setup, and I've attached them to their stands very well so that the speakers won't come off the stands, but that still means that the stands can be knocked over and take cables etc with them. Nothing I can do about that, but as they are rear speakers they're right at the back of the room and hard to get to in the first place.
Aside from nailing everything down, you can only do so much sadly.