Fences loom large in the human experience, defining what we are and are not. The Chinese built the biggest fence ever, known popularly as the Great Wall. The Germans giggled as they drove around that effete French fence, the Maginot Line. Without fences, history would be shapeless.

So too would our yards. Rare is the homeowner who does not want a good sturdy chain-link or redwood fence between himself and his neighbor, truly making a man''s home his castle.

"It''s a boundary thing," says fence expert Jack Benz, of Peninsula Fence Co. in Sand City. "People want to keep their kids and dogs in or out. Also, there are a lot of people who flat don''t want to look at their neighbors."

Fencing options for the homeowner are numerous, with various materials, styles and installation options just a phone call--and some hard work--away.

Constructing a fence involves digging postholes; sinking posts in concrete in these holes; and connecting the posts with rails and boards (hammering, hammering, hammering). While it can be done, it''s not easy.

"Homeowners can most surely put in fences themselves," says Benz. "But it''s not for everybody; it''s not magical. It can be back-breaking."

For those who aren''t up for the task, there are plenty of fence contractors locally like Peninsula Fence Co. that will do the entire job for you, from assessing your needs to construction. But for the industrious handyperson, Benz recommends a kit.

"We have kits on what to do and what to look for," says Benz.

There are also how-to books available at hardware stores, book shops and libraries. These manuals give a simple, step-by-step instructions on building the fence that''s right for you. For instance, the Sunset Guide titled How To Build Fences and Gates offers 22 choices of wood fencing, including everything from the wholesome white picket to elaborate bamboo or welded-wire options that look appropriate for POW camps.

Using your fence kit or how-to guide, you can design the perfect fence (typically six feet high, says Benz) that will accomplish your security and landscaping goals. After the design comes the choice of materials.

"The most popular in this area is redwood," says Benz. "Then there''s the chain-link, which comes in regular chain and vinyl-coated. Another option is pressure-treated wood."

The strength of a good fence lies in the posts, the vertical segments of wood usually set in concrete. If you don''t properly plant the posts, you are asking for trouble.

"We use concrete to set the posts," says Benz. "If you don''t, they will get loose and the first wind will blow the fence down. And we use treated wood. If you don''t use pressure-treated posts, your fence is not going to last very long," advises Benz.

According to Benz, the chain-link fence, once found in almost every backyard in America, is still used commercially, but is no longer as popular in residential settings.

"Chain-link fences are not always accepted in different parts of town," says Benz. "Pebble Beach discourages it. It doesn''t look very rural."

In his poem "Mending Wall," Robert Frost writes, "Before I built a wall, I''d ask to know/What I was walling in or walling out and to whom I was like to give offence." In fence building, truer words were never spoken. Before digging postholes and cutting boards, it is very important to know exactly where your property line lies so you don''t build on the property of the very person you want to keep out.

"You can''t believe the pissing matches that occur over putting a fence six inches on somebody else''s property," says Benz. "It all gets back to a man''s home being his castle." cw