Which of the following heights of fence deters only casual trespassers?

In established physical security standards, a 3-to-4-foot fence is low enough that a motivated person can step over or easily climb it, so it serves only as a psychological boundary marker that discourages people who have no real intent to intrude. It does not provide meaningful resistance to anyone with a deliberate plan to enter.

An 8-foot fence, especially when topped with barbed wire, is considered a high-security barrier that deters even determined intruders, not merely casual ones.

A 2-to-2.5-foot fence is effectively a decorative or boundary marker and provides essentially no deterrent value even against casual trespassers.

A 6-to-7-foot fence is difficult to climb without tools and deters most intruders, going well beyond the casual-trespasser deterrence level.