The same way you dispose of all toxic wastes. Put it inside a plastic bag, wrap it in newspaper then put that in the middle of a normal bag of trash.
If you want to be real careful wrap it in three small plastic bags and wrap duct tape around them. That should hold for at least a couple of centurys, by then it won't matter
One day a billion years after you are dead the planet will spiral into the sun and every molecule will be recycled into hydrogen.