It's not secret to anyone -- especially burglars -- that the sliding glass patio door is a weak link in the chain of security around many homes. The problem is especially important to me since my home has seven such doors. As a result, I've become increasingly interested in the various ways to make these doors less vulnerable to forced entry.

Sliding glass doors have three main weaknesses:

First, their cheap locks are usually made with brittle castings that will break under fairly light pressure from a prybar.

Second, many of these doors can simply be lifted right out of their tracks and set aside.

Third, they are made of glass, which in itself is very easy to break.

Surprisingly, that third weakness is not as important as it might seem. Most burglars will avoid breaking glass to gain entry to a home: It makes too much noise and poses the risk of injury. So if you take care of the first two weaknesses, you will have gone a long way toward upgrading the security of any sliding door.

WEAK LOCKS: A super simple way to get around this problem with many doors is to lay a board in the track of the moving door. Cut the board just long enough so that it jams the door shut yet still can rest flat in the track. In many cases, a burglar can slip a thin strip of metal between the two doors and pop this board out of the track. To prevent this, you can drive a sheet-metal screw down through the board into the track.

That's a cheap solution, but removing the screw can become extremely tedious if you use the door very often. For that reason, use the board trick only for doors that get very little use. For more active doors, try pinning. To do this, close the doors and drill a hole through the frames where the two doors overlap. A 3/16-inch hole is the right diameter for a 20-penny nail. Caution: Not all doors have a frame wide enough for this technique. Examine your door carefully to make sure you can drill the holes without hitting the glass. If the drill hits the glass, it can crack it.

If neither of these two do-it-yourself security measures is right for you, consider an add-on lock to back up the one already on your door. One type is the Deerfield Patio Lock (Deerfield Lock, 758 Hoffman, Deerfield, Illinois 60415). To install it you drill two holes in the fixed door and two in the sliding door. Studs on the lock body fit these holes, and turning the key locks the body in place. The lock is unobtrusive, but mounts at floor level so unlocking and locking require stooping.

A bar-type lock such as the Charley Bar (Charley-Bar, 333 West 195th Street, Glenwood, Illinois 60425) can be mounted up at waist level, where it's easier to operate. It's essentially a strong metal bar that prevents movement of the sliding door when locked.

UNTRACKING: To prevent a burglar from lifting your door out of its track, you'll need three sheet-metal screws about 1 1/2" long. Open the sliding door all the way and drive these screws up into the top track. Position one at the middle of the door opening, and the other two a couple of inches in from the edges of the opening. Drive the screws in just far enough to clear the top of the door when it's closed. The screws will now act as stops, preventing the door from being lifted up and out of the lower track.

NOTE: The top rail on some doors will not have a flush surface to butt up against the heads of these screws. Instead, the rail will have a U-shaped cross section. If yours is one of these doors, fill the channel of the U with a snug-fitting length of wood. Q: I built a cabinet out of particle board and covered the outside with Formica . To save money, I painted the inside with latex enamel in a matching color. Two questions :

The particle board inside was smooth before I painted it, but now it's rough, almost pebbly. Why?

My neighbor says I should have used Formica inside as well as out. He claims using it only on one surface can cause warping. Is he right ? A: The rough texture after painting is due to your choice of paint. Water-base paints make the bits of wood fiber in the particle board swell. For that reason, it's best to use oil-base paints on particle board, or at least use them for a prime coat.

As for warping: Particle board is a fairly stable material. You probably shouldn't have any warping problems, at least not for the main body of the cabinet. If your cabinet has large doors, there's a chance that they might warp since they're not supported along the edges. If so, it will be easier to make new doors than to try to straighten out the old ones. A couple of readers have written in with tricks for making their own firewood by rolling newspapers into logs. The first is to use the wire made for tying plants to bind the logs tightly after rolling. This wire is a lot like the twist-on ties used for sealing plastic bags, but it's sold in garden stores in long rolls. It's easy to handle and so fine it all but disappears as the log burns; no heavy chunks of wire remain in the ashes.

A second reader binds logs with ordinary string, then stands them in a wash tub and lets the water from the washing machine drain-soak them. After the soaking they're stood on end outdoors to dry. The soaking binds the paper layers together and produces a longer, steadier burn.