They wont be that deep, most of the time during the summer seems like guys are running them 50 to 150 ft down. You can also jig for them if you find them stacked up on underwater features closer to shore. I have heard spring time is a great time to fish for them by the mouth of the Clark Fork. Summer they seem to move around the islands or over by the Monarchs. I got very eager to try fishing for them a couple years ago and used the Fish and Game website as a great source of info on Lakers. They release a "State of the Lake" and it has detailed info on spawning patterns, summer patterns, trap locations, etc.
That being said, they have been actively netting and offering bounty's for them in an attempt to rebuild the Kokanee population, and the Laker population has dropped a bunch. They are not as plentiful as they were 5 years ago.