"The reason is that we have business development people who are very aggressive about going out and knocking on doors, talking to people, and asking people for the order. It's that simple," Clark said.

This approach is essential in his current environment, he added.

"Literally every financial institution in the entire world has a branch in Washington D.C., because this is where they print the money," Clark said. "So, the landscape here is more competitive than anyplace else in the country. That means you have to really reach out to people or your business development and membership growth just aren't going to happen."

Clark said that the credit union had been doing so well with one business development representative the decision was made to add a second one in late 2013. There was just one problem: Two very strong internal candidates applied for the position, one a teleservices representative and the other, a member service representative.

"We knew we eventually wanted to hire a third one," Clark said.

So, he convinced the board that it made sense to move both employees into business development roles at the same time rather than wait.

"It sent a good message to other employees," he added.

It's a decision he hasn't regretted. Clark also said that it's no coincidence that these two positions were filled internally.

"No matter what the position, we hire people with the right attitude. We make a conscious effort to hire people who are member-centric," Clark explained. "No twiddling and no cell phones. We look for people who are warm and friendly, but still aggressive."

Clark said he's already identified two other employees who he will likely move into a business development role at a later date. He predicted that all future business development positions will be filled internally, as well.

Read more: You can't win new business sitting down …

"When my business development team is at an event with other financial institutions, they never sit down behind their table," Clark said. "Instead, they stand out in front of the table so that they can greet people as they come by. They never sit down."

He said he's seen business development people from other credit unions who sit behind their tables and hardly interact with anyone.

Once, DOCFCU's business development team was walking back from one such meeting when they happened to pass by a nursing school. According to Clark, one of the business development representatives excused herself from the group and entered the nursing school. She subsequently located and spoke with the HR director.

"Now we have an event at that nursing school every month," Clark said, pointing out that little extra efforts like this add up to a big difference over time.

While he isn't complaining about the tremendous success of the credit union's business development group, he does admit to one mistake.

"When you bring in that many new members, you have to be able to serve them all."

As a result of DOFCU's growth, service levels were not quite where he wanted them to be, nor where long-time members expected them to be, Clark acknowledged.

To correct the situation, the credit union is undergoing an internal restructuring designed to accommodate both current and future growth and ensure that service levels are kept to the DOCFCU standard. The credit union currently has 37 employees and may add as many as 19 more in the coming months, he said.

In an environment where business development is the chief growth driver, marketing is used primarily for existing member outreach.

"Marketing has helped our members to relate to the credit union, primarily through the newsletter, which we try to make very personal," Clark said. "This year, our business development representatives blew their goals out of the water. The numbers make it very obvious that they know exactly what they're doing."