I have the same problem with my Ficus tree and based on my experience
I don't think adding a few rocks will help during a thunderstorm. I
actually had the Ficus staked and last week a storm blew through and
pulled the stakes out of the ground.

What I wish someone would sale is a pot support that I could put the
pot in. I can picture it in my mind but I am having a hard time
describing it. What I envision is 2 rods bent into a circle, the top
being smaller than the bottom. The 2 would be connected together with
identical length rods. The pot would go into the top circle and would
fit snug just under the top lip.

If you are having trouble visualizing what I have in mind just think
of a regular flowerpot with the bottom cut off and then turned over.
The pot with the tree would then fit into the other pot.