The fence is someone that knows the plugs and the people that are buying the product

Got the covid-19 vaccine

The fence is that little piece of skin that separates the the playground ( her vagina) from the dump (her anus)

The definition is simple. Someone who is described as 'The Fence' is either so afraid to voice their opinion as to not hurt someone's feelings OR they simply don't have opinions and therefore agree with both sides. They are not 'sitting on the fence' as that implies they are still considering both sides of the argument. People who are 'The Fence' are so non-committal that they straddle both sides with such parity that might as well be hammered into the ground with some panels.