Prusiks. I have tried the so-called Bachmann knot as well but they did
not work well on muddy rope although easier to "break". I tried one
other but cannot remember its name. I can tie prusiks with my eyes
closed or in total darkness (being a caver) and have climbed many
thousands of feet on them including out of the worlds deepest pit.
BTW, it better be three prusiks, not two. You need one for your chest
and one for each foot although in a pinch you MIGHT get by with a
single one for both feet.