One thingsyou can do relatively inexpensively is have the location scheduled onto your homeowner's insurance (additional premise endorsement), assuming you own an insured house elsewhere. This will allow your secondary property to use the personal liability limits of your homeowner's policy. This does not insure any property (barns) on your land but does protect you up to the limit if someone gets hurt and you are liable. This typically costs nothing or very little to add on. Coverage here though might only be $100K-$300K.
Best option is like BOBO said, also purchase an umbrella policy. Most companies require you to have your auto liability policy (since that is the most likely thing any of us may do to become liable for something in our lives)maxed out. Maxing out is typically $250K or $350K in auto liability insurance, way above the state minimums. After you have bought that maxed out policy then you can buy an umbrella policy. I have all my policies with Farmers but tons of other companies can do this for you and some companies (like Metlife) will likely do it separately.
It cost me about $300 extra per year to max out my auto (in addition to what I was paying for state minimums). All depends on number of drivers, sex, age, etc. I have three drivers.
The umbrella then cost me about $350 per year for $1,000,000.
Let me know if something I have tried to communicate is not clear.