I added some braces on the outer part the other day, and under the floors, above the rockwall, and the base have braces to hold everything square. I also put multiple screws keep it from parrallelagraming (nice terminology, lol), a LOT of screws would have to pull\break out for it to change shape. I know what you're saying though so I did add the braces a few days back for good measure. They aren't very big, but they'll hold it square. In the pictures it wasn't quite done yet. I called around and apparently it's hard to find a 12 foot 4x6, but I can get a 16 foot 5x5. I'm going to go that route and add a tire swing on the outer most part. The guy who built this thing originally was an idiot. I've found screw tips poking through wood and kid's height...next to the SWINGS, jagged wood sticking out, etc. He used 3 inch screws going through a 1x6 and 2x4...dumbass. That's all fixed now though...except for the wood above the swings. I also picked this up today while I was at the junkyard for $10. Not sure where I'll mount it, it'll probably be up in the new section, facing the rear:
