Kayaking Resource

I am looking for a personal gps unit for hiking and kayaking. I saw one not too long ago that works very very simply. You turn it on and mark your position when starting out and it tells you how to get back. That’s all it does. It is meant to be worn on a jacket zipper or a lanyard. Can someone tall me where to find it or suggest something else? Thanks in advance.

I mean when you do it right, like the sprint kayak competitors. Not like taking a leisurely paddle on the river.

I am a rower but I cannot afford my own shell to practice in by myself. I know rowing works more muscles, but would kayaking work muscles that matter for rowing or is it all just arms?