We all need support!

 I have always attached the legs to all of my previous layouts and I see no reason to change.
Liking to keep things simple, a method of keeping the legs in place is one that I came across quite by accident a long time ago.
With the legs attached by hinges to the end of each board- one board has two- a way of keeping them in position was considered. Enter the humble screw block available from most DIY outlets at very reasonable cost- these are the things that keep flat pack furniture hopefully at right angles and therefore square.

An elongated Z shaped bar is produced with 3mm diameter rod which has each end bent to a right angle, preferably in the same plane!
These rods are them simply inserted into the blocks which keep the whole lot upright and rigid.
There- said it was simple.