The 15 ft fence may or may not do it
In my case even if the "gate" was 15 ft or 20 ft (30 ft?) Clover would lumber jack (sort of like Quarto drive) climb right over it.
I'm not sure if it's possible to give a puppy dog enough exercise to satisfy it. Seems their batteries recharge fairly quickly when young. Plus the more important factor is the sense of "freedom" they have. In human terms one would think an acre of land with a few acres of woods behind it would be enough for a dog. But from the dog's point of view they are thinking in terms of territory as big as they can roam which could be as large a mile (depending on what other dogs are around). The intoxifying feeling of being able to roam free is just too much for some dogs. That's why it's so hard to break them of the escaping.
The one poster has a good point on chaining inside a pen. Make sure the chain isn't longer than the distance to the perimeter, and the dog can not drag the anchor close to the fence. I wish I could still use that as an option, but with another puppy in there the chance of injury is too great.
I'll tell you what we did...
When Angus was a pup (also a rottie) he started climbing over the fence too. We ended up getting an electric fence (not the invisible type-he would have went right through it). All it took was one time getting shocked and he never tried it again! It's cheap, easy and works!