Garmin 66sr Off Trail Routing?

I've recently picked up a Garmin 66sr GPS. I can't seem to figure out, if even possible, how to simply create two waypoints and then tell the unit to route directly between the two points without using trails or roads. Right now it's routing on dirt roads.

I want to route between two waypoints directly. I went into the setup and routing settings but can't figure out a way to do it, even with reading the pdf user manual. Each time I restart the Navigation, it routes on the roads or dirt roads.

Do I need a different map? Do I need a different GPS?

Here is an example scenario. I'm helping a friend look at large properties that he wants to retire on. We have plat maps and have located multiple property markers (metal rods in the ground). We want to use the GPS off trail / off road to help find other property markers for corners as well as once two corners are found, to select two of the waypoints and then route/navigate between the two and walk the "property line" to understand where the property lines are and any unusual things we might find on either side of the property lines.

These properties vary between 20 and 160 acres. Distances between waypoints can be between 1000 feet and a mile.

Thank you in advance if anyone sees some obvious points to help with. So, we really can't plot this offline on a map. We use plat maps to find one or two of the property markers and then from the plat map, you can enter a bearing and distance which helps us to pinpoint other corners. Once we find corners, we will walk all sides of the property lines.

 

Select setup then routing & allow direct routing. Now when you create a route you'll have a line between the waypoints, distance and bearing.