If you stop at the french drain, how wide is the gap between house and last post? And is the french drain up against the house?

My only thought is to drive a post-holder spike into the ground as support for the post that's against the house. Personally, I'd space the posts so that there is a short run of fence crossing the french drain. IOW's, the post next to the house isn't a major supporting post but the post on the other side of the french drain is.