Electric fence
We had to enforce our 6-8’ privacy fence with electric fence to keep in German Shepherds. We bought short 3’ t-posts, battery, electric connectors, – even signs! --etc. Our backyard has some open areas, some woods and this fence was easy to install. It ran parallel to the existing fence for the most part. I swear our dogs learned to read “electric fence.”
It did the job, fairly easy to put up and way less expensive and less labor-intensive than an underground invisible fence option. If the invisible feature is important to you, though, our electric fence solution won’t appeal to you.