I am getting a contractor to put me a garden fence up in my garden, he has sunk two 4 x 3" posts 84" apart, is this enough, the fence is 8ft 6" long x 7ft high with a gate 48" x 84", it will have vertical boards with no gaps in between. i am worried this might not be strong enough in strong winds, i thought it might need another post. any thoughts on this guys ?