I am sorry but you have no clue as to how many agents it would take to effectively seal off an entire golf course to effectively deal with any possible threat. In an ideal world, they would have 500 agents available at a moment's notice to do so. Nobody in their right mind would want that kind of job because it would be so incredibly boring. The entire process is a balancing act, where you have to account for the threat and how effective your protection can be. In the first assassination attempt, the coordination between the Secret Service and local cops was non-existent. There were sufficient personnel present, but it was a total cluster ****. The second attempt was foiled and the Secret Service did their job. My greatest fault fell with the local sheriff who is obviously a Democrat who said Trump was not the sitting President so he and his people should not be concerned as much.