Help How to properly secure plastic bag?

[spanishguy22]

I'm really digging the plastic bag method but I need to know how I came make it really secure so that it won't break if one were to fall or struggle. I don't think a cord tied around it is safe enough.
How could you secure this method? Could one use several bags tied after another for reinforcement? Thanks

 

[calendulo]

Dos casos de muerte debida a sofocación por bolsa de plástico

Maybe you could find out helpful information here, or maybe not.