Break it in 3 phases - 1 month, 6 month & 12 months. Tell them what you'll "do" in 1 month and then tell them what they'll "get in results" after 6/12 months. Map results to their revenue/traffic.

Now give them an irresistible offer - if they extend the contract to 12 months within 30 days of signing up , they get X,Y,Z extra worth $XXX. These free things can be landing page's conversion optimization, paid media buys every month, monthly press release for media exposure etc. Think what else might help them as business an club those in free package.