"thats why they are known as fence busters: the momentum of the rotary cutter will overpower the brakes...in other words you put the clutch in to stop and the rotary cutter will still "push" you even though you have your foot on both brakes...."
They certainly will.........unless you buy a cheap, simple
PTO override clutch that prevents this. They are very common, I've never run a
PTO implement without one, and they work nearly flawlessly with routine maintenance and care. It's a $50-60 part that makes those $2000 tractors very usefull today versus much newer and more expensive tractors.
PTO Parts (Coupler, Clutch, Adapter, Increaser)