A low fence is more of a decorative item than a protective feature. Any wall that can be easily climbed or even stepped over will do very little to protect a house. For tall fences, the material used to construct them will determine their scalability. For example, concrete panels are more difficult to climb than a chain or mesh fence. Adding a trellis or barbed wire is an effective way to make a fence even more difficult to climb.
Gates in fences remove the need to climb them. A gate is effectively a hole in your fence that anyone can pass through unless the gate is locked. A sturdy lock is essential for a fence to protect a house when a gate is present. The gate should ideally be the same height as the rest of the fence; otherwise it becomes a low point for intruders to climb over more easily.
Different types of fences offer different levels of protection. Plastic fencing is a basic form of fence that will offer little protection from anyone who really wants to get past it. Mesh fencing is more resistant but can be easier to climb over, with the mesh providing effective footholds. Concrete slabs held in strong, reinforced concrete posts are very sturdy and can be angled to make climbing difficult.
Fences come in a variety of heights and materials, providing a varying level of security and also a varying amount of aesthetics. Short, brick walls with wooden fencing on top are favorite choices for around gardens but the low brick portion is easy to climb over while the wooden sections can be easily damaged or even removed by intruders. Conversely, high concrete fences offer more security but are less pleasant to look at.