teach me about fishfinders

Are there certain models that are considered best for Kayaks? I have never used a ff before and have no idea what to look for. Remote battery vs batteries that go in the ff, do I have to cut holes below the waterline, Features, Durability anything else? I don't care about bling but I want a good, durable ff.

I haven't fished from my yak yet but I'm going to Amador Thursday/Friday and hopefully Sand Diego for Thanksgiving. I mounted my Scotty swivel this weekend and that went well.

 The Eagle 245DS is a good dependable basic fishfinder around $100. You can spend a lot more if you want color and higher resolution,3-D, side imaging, etc.
 Most guys run a small 4-6amp hr. battery(longer time between charges but heavy)or a new school AA battery pack (for lighter weight but shorter charge life). You can get the FF as a portable (self contained battery)if you switch yaks often. Or drill a couple holes for a more permanent mount with the battery and transducer inside the hull. If you do the "pool noodle" type transducer mount with removeable though hull fittings the FF can still be switched from yak to yak.
 There are many posts on the subject here and on other kayak boards.
 Feel free to ask away,everyone has a slightly different take on the subject.