A fencing device 1 comprises installing means for driving the posts 5 of the fence into the ground. These posts are provided with a pointed lower end 9 so that they can easily be driven into the ground. The net with the posts attached thereto is wound on a reel 11. The installing means gradually guide the posts from the reel to the ground, while the lower ends of the posts are driven into the ground. For guiding the posts, the installing means are formed by a guide consisting of a top guide profile 13, two side guide profiles 15 and a bottom guide profile 17. When a temporary fence is erected, the first post is to be driven into the ground manually and supported with a cable or pole. Subsequently, the fence will be unwound from the reel while the trailer is moved on.