Fish Finder On Deck.

[mtnbykr2]

I don't think there is a "rule" as to where to place the unit, but do keep in mind "paddle stroke" and clearance , then there is the "reach", can you reach it to change settings, can you see it well?, and is the spot on the deck solid enough to mount it, that's about all I can think of there....
Try placing the unit in different spots as you are sitting in the yak and see what best fits your fancy, and always remember "measure twice, drill once", but double check yourself after you measure twice...lol
I just thought of one more, keep in mind that this may not be the last meter you install on the boat, so be mindful of how much and where you drill/cut...hope this helps, also there are boat loads of examples on this site...and lots of expirience...