I need a simple device to figure out where the sun will be in the sky at any given day and time from any location on my property.
My idea is to have a smooth wooden pole, maybe six feet high, with a large protractor attached to the top. The protractor would be attached to the post by a nail through a hole in the exact center of its arc. A piece of PVC pipe would be attached to the top of the protractor to look through. Near the base of the post a disc marked in 360 degrees would be fitted around it. So, once I found true north and south by lining up straight poles at true noon, I could use charts of the sun's altitude and azimuth to find the sun's position. The post would be placed and leveled. The bottom disk could be rotated till the whole device was a certain number of degrees away from true solar south, and the protractor could be moved up or down till it pointed to a certain altitude.
Of course, I would be careful to avoid looking at the sun through the PVC!
Then I would be able to tell if the sun would REALLY clear that tree on noon of March 21st! (Or whatever.)
I think your idea could work, and you may be interested in RimStar's DIY elevation/azimuth tool guide; it explains how to build your own elevation/azimuth shade finder. Building off of that tool, a simple sun line up tool could be mounted on to the top protractor of the elevation.azimuth shade finder to avoid looking at the sun directly. Here is a short YouTube video by RimStar explaining how to build the sun finder tool: