In direct mail houses and advertising agencies a popular rule of thumb is to orchestrate "touching the prospect" at least five times in order to be remembered. It's a good rule. In those circles, "touch" represents anything you can get in front of the prospect, like an ad, a mailer, a letter, a radio commercial, etc. In professional services I believe the same rule of thumb should be honored; with a twist.
"Touch" in professional services marketing needs to represent physical presence; first-person contact with people you are targeting. We all know our success comes from creating and sustaining first-person relationships... and "first person" = "in-person".
If you want a shot at getting new business, or maintaining existing business, find ways and places to be seen, in-person, by those you are targeting.