Here’s a few brief bullet points about why you need a long term relationship with someone with digital expertise :

Constant Connections
Only someone embedded in the digital scene will have the latest info on partnerships for your brand which are outside your vertical (eg everything from payment technologies to data mining).

Up to date techniques
Best practice in digital marketing changes all the time. Only by regularly engaging with digital expertise can you hope to be at the leading edge.

Trial and error
Rome was not built in a day. Similarly, great campaigns often need time to evolve. Often, only repeated iteration gets to a viable campaign, and for that you need a sustained relationship.

Sanity Check (avoiding pitfalls)
As you go along, you’ll have your own ideas, and develop your own skills. However, it’s very useful to have a sector expert to ensure you don’t miss obvious opportunities, or make dumb mistakes.

External perspective – fresh ideas
By having a part-time digital expert, you’re able to get easy access to an outsider view. This can help you avoid getting stuck in a rut, and keep your thinking fresh.

Personal support
Business is a roller coaster. Sometimes you’ll be too timid, sometimes too reckless. Having additional strategy and management brains in your team helps smooth the peaks and troughs, giving a more consistent performance.