if you wanted something really heavy that could either be hard to tip over or tip over and kill someone, those stands i gave the link to are fillable so you could put sand or lea shot or something in there that would probbly add another 30 pounds depending on what you put. and also some BLU TACK would be good for anchoring the speakers to the stands. the place i know sells it is www.audioadvisor.com

Haoleb's Audio/DIY Website