Open Space: Fence

Hello, I'm trying to assess how much of our project site qualifies as open space. A large percentage of the site is extensively maintained grass and woodland planting, however there is a security fence separating the buildings from the green perimeter area (which is generous). There is green, open space on both sides of the fence, but the areas inside are accessible only to staff. My question is, does the open space on both sides of the fence count for the credit? Or does open space have to be publically accessible? Thanks!