Well, I actually ended up ordering one from Amazon for $35....used some "free" credits I had. Somebody out there manufactures them for monitoring streams and ponds. They have several sizes for depth and width and got good reviews. I am going to incorporate the ideas shared. Will fasten it to a post and have the post fastened to a cinder block or equivalent. I guess I will have to establish a "base line" to record current depth and then can judge from there. My pond is shallow where this will be located so I purchased the 4'-8' version. Sorry I am not smart enough to paste a link for reference.

Thanks!

John