>>Oddly enough, I've noticed that my auto-siphon does a great job of not getting any tub into it. Not sure if you have the same one but it has a little ...well I don't know what to call it... it has a "thing" on the end that seems to prevent the cake from getting sucked in. It actually rests pretty well on top of the trub and seems to suck up everything above it.
My trub is not so solid that it will prevent the auto siphon cap from penetrating. When I lower the siphon (after racking more than half of the beer) I will eventually "pierce" the trub, and the siphon end cap hits the bucket bottom. The flow of wort will stir up sediment.
What I do is pay close attention to the color of the wort being racked. Any signs of whiteness and I pull it up.
You can also help yourself by placing a wedge under one side of the bucket, causing it to rise on the other, then siphon from the deep side.
I find the clip that holds the auto siphon to the bucket to not be strong enough, so that I must hold the auto siphon with my hand, even when the clip is on.