Tying plants down? Subwassertang & Fontinalis antipyretica

[Furby]

I was wondering if there is anything I can use to tie down subwassertang and fontinalis antipyretica that would hold them against a surface long enough for them to attach (if they will even attach) and then have the tie either dissolve or fall apart. And if so where to get it. I saw a video that said organic sewing thread would work but I don't know where to buy it and don't know if it would eventually disintegrate. I would want it to disintegrate once the subwassertang and fontinalis take hold. I would be attaching the subwassertang to an upside-down clay pot. I have a piece of driftwood that I am undecided about what to put on it. I have narrowed it down to 3. It will either be: 

A. The fontinalis antipyretica

B. Hookeriaceae sp. (Image attached)

C. Riccardia chamedryfolia

The wood that it would be going on is the one in the picture of the tank that I have attached. If I go with the fontinalis antipyretica I would start at the bottom of the wood and tie it down and then train it going up the wood tying it as it grows if it needs support or doesn't attach itself. I am kinda hoping that it will attach itself at the bottom over time and that it will either attached itself to the wood as it grows up it or that I could tie it as it grows and it would eventually attach and that the tie would eventually dissolve or disintegrate and fall off. Any thoughts and/or suggestions?

[lefty o]

any kind of cotton thread would rot and dissolve after a short time, how long i dont know. id try a fabric/sewing/hobby type of store to find it.

[Furby]

Jo-Ann fabrics and crafts? They have cotton thread but I don't know if it is organic. Once the cotton thread starts breaking down, will it foul up the water?