My new test area
 

So the other half had the idea of clearing out a small area behind our shed that was wild and overgrown. I was happy to oblige as I saw this as an ideal area for a little crawler course.

This is the result of mine and my boys labors "thumbsup"

What we pulled out and what we were left with. Just need to import the rocks, branches for a steep ascent and pallets to make the course/test area.

great work,

I built a rockery/play area in our garden about a year ago, great for a quick play time and testing, got lots of rocks off of ebay for very little (about 1 ton or so).

I reckon your half buried sink will be the best obstacle!!