I used the spring approach on my DIY trailer. It's worked perfectly for 3 seasons of use.
I've beat it up too. Loaded the trailer with so much junk one ride that I bent the "arm" that goes to the hitch.
I've also flipped the trailer (empty) several times, bombing around bumpy corners, or jumping off curbs. No problem!
http://www.metrompg.com/posts/bike-trailer.htm
