Stay in touch with executive recruiters when you are employed.
It is always difficult to build on a relationship with someone when you only really speak to them when you need something. It doesn't matter if it is someone who only calls their "friend" who owns a pickup truck, when they need to move something, or the sales guy that only calls on his small accounts when he is desperate for orders because his big customers are not buying as much.
This also applies when working with executive recruiters. The candidates that make an effort to stay in touch and to keep me updated are the ones that I instinctively contact when a client gives me a mandate. If it is not an opportunity for them, they often know someone in their network whose career they would like to assist.
As a side note, I also remember the people that thank me when maybe I did not help them land their new job but maybe I was able to offer some sort of lead or piece of advice along the way. These people tend to be polished people persons and are the types of personalities and positive thinkers that others tend to want to spend time around both personally and at work.
Executive recruiters have a good understanding of the pulse in the market and they can be a resource for you for things such compensation comparables to help you with your own employer negotiations. I am not recommending people suck up to executive recruiters (they are the least likely to fall for that approach anyway) but stop trying to build relationships with search professionals only when you are unemployed.
Farewell,
Mike