When someone askes you to take them, explain that you don't mind, and that you like having the opportunity to help them learn, but the next trip out you already have some plans for the next trip out, a specialarea or some strategy you are wanting to try out, but to give you a call and the two of you can set up another time that would be good for the both of you.

That way you are not brushing them off, and they will begin to understand thet your every free moment is not to be their personal guide and trainer.

Good luck and God Bless