This weekend I caught about 15ish chum, maybe a couple more. Of those 3 were foul hooked (dorsal fin). The rest were all hooked completely inside the mouth. This was also fishing in some VERY thick schools. The trick I have found is I rarely do a traditional hookset. Often when retrieving through a school you'll feel resistance which is normally the fly bouncing of chum. When I first started at this, I treated every bump as a bite and set the hook. This lead to many more foul hooked fish. After a while you can start to tell the difference between bumping fish and a true take. However, I basically just stopped setting the hook. I continue my slow retrieve until the a fish is on the line then start playing it. I never jerk the rod or do hard strip sets. I might miss a few light takes this way, but end up with fewer foul hooked fish. As for getting them to take, like Nick said change up the fly until you find what works. Have lots of patterns to try. Once you feel that you have shown your fly to lots of fish with no success, tie something else on. If the fish are in big schools, I usually cast to them for about 15 minutes then switch until I start catching.