Years ago (when my eldest was a toddler) aunts, uncles and cousins said I should get a website and tell people about line training... Well, here goes. 

"Line training" is my variation on blanket training. Freedom for me, and safety/ freedom for the wee one:

Purchase several yards of inexpensive nylon webbing (like dog leashes or backpack straps are made of) to outline boundaries. The webbing comes in many colors––choose one to use consistently. We buy ours at Ace Hardware.

Straight segments of the "lines" can be placed on the floor across the doorways or wherever you wish to signal "do not cross". (The few rooms in our house with a blue line continually taped on the carpet in front of the doorway have has added value as a conversation piece--makes guests ask questions.) You can make a blanket sized square by safety-pinning the corners together. My diaper bag always contains one "line square" (blanket sized outline that is safety pinned at the corners), and a couple of straight segments big enough to define a doorway or stairway.

Unlike playpen time it requires the child to exercise self discipline. We like the versatility––the child can access a little square of space, a whole room, all but one area of the house, whatever! If I’m doing a big project, I can either keep the child in the room with me, or in the adjacent room––in my sight, but OUT from under foot, depending on the need. All without those cumbersome baby gates.

Lines are especially useful at the top of a staircase––I’d put it back a foot or so from the stairs though, as they tend to come to a SCREECHING halt when they see the line, and the force of "braking" so suddenly could cause them to loose balance.

Because of the portability, it is great for visiting other's houses too! If we were visiting in the living room, I'd place one of the "lines" on the floor at the doorways, and baby would be able to play freely in the room w/ us, but would crawl up to the line and stop! Our babies are allowed to be carried across the blue lines, but not to cross alone. (Around age 2–or when I’m expecting another baby and too tired to pick them up for this--they can get verbal permission to cross.) (Someone on a different board was concerned that the child would substitute obeying the "tool" (lines) for obeying the parent and would be confused about what to do if mommy told them to cross the lines–wanting to "obey the lines" over obeying mommy. I never had this problem. I've even had a 6 month old comply with a grin if I say, "You may cross.")

As far as the training process, I put the child in the "line square" and give him something to play with that he wouldn’t usually get. I stay close at hand with a little switch. The INSTANT the baby starts to cross over the line or put a limb over even slightly, I place the child firmly back withing the boundry, tap the LINE with the switch, and say, "No." (With a toddler you could say, "No. Don’t cross the line."

Our babies start when they first learn to scoot purposefully––––about 5-6 months (though you could start later, I’m sure). For the first 1-3 weeks I do 1-3 sessions per day 10-30 minutes per session with a blanket sized square outline. I try to do at least 3 (if not 5 or 6) days per week at first to help make sure the concept "gels". With baby inside the square, it is often helpful to flick each of the four "lines" while gently saying, "no cross" to help the child understand. Usually after 2 or three sessions the baby/child understands but objects loudly, so I start adding in spirit training. This "advanced line training session" is not over until baby is happy and obedient for 5 minutes or so.

When I use the small square instead of a whole room, I often give special toys. A jar of marbles (only if yours won’t eat ‘em–––they could be a choking hazzard) or a bunch of empty thread spools, craft feathers... something not usually offered as a toy. I’ll often put on music, etc. I don’t want to send the message that this training is punitive.

Once they’ve mastered the concept with the small square, I rarely use the square except for the occasional reinforcement at home, or when we are out. I find straight sections of line marking of a doorway more useful for daily use.

If you choose a bright royal blue as your "line" color, as we did, painter’s tape makes excellent boundaries for the doorways and other semi-permanent locations. Because it is, by design, low adhesive, it won’t gum up the carpet as badly as regular masking tape.

I was amazed at how much the line training carries over into other areas of obedience and self control. If I notice the little tyke not obeying on "no touch" and other things, a round of the "advanced line training" (with the small blanket-sized square) seems to reinforce parental authority and the child will be back to cheerful obedience quickly!

Now for the disclaimer and confession! Keegan has been my most challenging to line train. He’s 10 months old, and still has a ways to go. He doesn’t get the willful defiant look the girls did when he crosses, but rather neglects to ‘remember’ the rule. Attentiveness to rules, however, is an important skill, so he’s NOT getting off the hook. It is time to vamp up his line training!