I tied down fishing line a third of the way down my plant and now two weeks later the growth in the stem made the line sufficate it, and snap off. So I pretty much have a third of my plant gone and its topped now... great.
You can also try to use ties like the ones used to close a loaf of bread(but longer ones can be purchased) They are more sturdy and won't tighten up around your plants like fabric or fishing lines. Go to a gardening store not Bass Pro for future problems just messing with ya.
You can use FL, as long as it's 250 lb test or better,lol. Regular line 6-12lb is like a razor to a stalk. I've used everything for screens in my scrogs and find regualr old wax coated string to work best. Twine is ok but it gets all in your bud like cat hair. A topped plant is a beautiful thing,...as long as you are still in veg. This could have been an act of the grow gods,....showing you the way
I second the use of bread ties, but I use a similar substance, and that's wire. Why? Wire doesn't rust. Cut myself lengths of it, and make a stretched long "U" shape with it, and secure the plant to the soil by pushing the two sides of the "U" over the stalk and into the soil. You make it relatively long because as the plant grows, and the stalk expands, it allows the wire in the soil to give and allow width in the stalk growth.