Depending on trailer weight and type, I've often thought of having a removable tow bar/hitch assembly. Something bolt on. This in combination with what others have said would mean that the thieves would pretty much have to come with a forklift large enough to abscond with the unit.
I see a guy on Instagram in Maine named Matt Rinard with a setup like this. He seems to really have the solo machine assist work flow down. Really cool setups.
https://www.tree133.com/team
Craig Bachman may offer this service. I have no personal experience, I just enjoy his presentation style, passion and commitment to knowledge in arboriculture.
Re reading my post I should have worded it along the lines that you did... Those roots were likely non existent above ground, previous to this project. Either the tree's root flare was already buried pre project, or perhaps they are incredibly vigorous adventitious roots that sprang up after the...
It's interesting to see those 1"-2" dia roots in that photo. Given their size, I'd imagine that they were there at a similar size before the backfill. Does anyone think those are new, post backfill adventitious roots?