Yes, a coyote will jump a 4 foot fence like it is not even there. I lost a pygmy goat this way a year ago. My yard was also 1 acre. I built an internal safe area for them to spend the night. 25x25 6 foot horse fence with an apron to prevent digging. A coyote can still go over a 6 foot fence, but the multiple barriers kept them safe (or relatively safe). I have since moved to a place with more land and more coyotes. I built a similar safe area but also surronded by electric. If you do electric, put it out a couple feet from your fence. They will hit it first and the added visual barrier of the 4 foot fence behind will keep them at bay