Just assembled the cat tree..so easy and is sturdy.  Don't think they will tip this over.  My cats could not wait for it to be done, they started clawing at the sisal almost immediately. The only suggestion I would make is the IQ box....there should be one larger hole at the top to drop the balls through and other holes should be a little smaller so they cannot get the balls out so easy.  I have chased the balls several times and put them back.