They sell these extenders online at Drs. Foster & Smith. They anchor the tall cat trees to the ceiling. Would that help?
yes I bet that would help... I will look into it. thanks.

I store cases of cat food and extra litter boxes on the bottom shelf of my cat tree, though come to think of it the fur-kids have 'tamed down' a lot in the last year or so. I don't remember the tree rocking since they were high-flying kittens...
good idea!