Zombies definitely couldn't climb fences
I might be misremembering, but I didn't think the zombie actually got over the fence but sort of made a half-baked attempt to get over the gate, failed, and then the walkers knocked the fence down.
They certainly didn't successfully climb the ladder early in the episode either so I don't get the feeling that the zombies will be able to overcome a fence that isn't easily pulled down by the weight of the crowd.
As for the "affair" between the wife and friend........I really
hope that is dealt with and over in an episode as I could sincerely less about a love triangle in the context of an apocalyptic zombie story. I didn't care for them in Lost and I certainly don't think this series will benefit from their use beyond just being an easy crutch for writers to lean on for easy story-telling.