These are the most ingenious planters I have found to date!  I had  been debating about what to purchase to replace the planters I already had.  They were still good, and even though they saddled over the deck rail, much like these do, they would fall off the rail whenever there was a strong wind or someone bumped into them.  These are adjustable and they also have a moveable type of slat that goes flush to the rail to ensure stability.  These planters are not going anywhere unless you physically remove them yourself.  The added plus is that you see beautiful flowers on both sides of your railings, so you can now appreciate the beauty both coming and going.  Who wouldn't want that!