Thanks everyone!

I'm glad that I'm not the only one experiencing this. I guess we still don't know exactly what is causing it, but it is extremely comforting to know that many others have experienced slipping and not only survived to tell about it, but still enjoy tree climbing!

Patrick, I don't know if size has anything to do with it or not, but I can certainly second your statement that a Blake's hitch never seems to slip on a Sportline. And, I'm going to cinch up a little before descending, too.

Icabod, I agree that it likely isn't the bark; I always use a sleeve-type cambium saver or a false crotch. It could be the ground. The ground where I most recently had the problem was buried under a thick _layer_ of leaf mulch and sword ferns, along with some rotten, moss covered logs, all covered with about 7 feet of salmonberry bush and devil's club. However, under my "practice tree" is mostly just bare dirt, and even though I use a rock-climbing-type rope tarp, the rope still gets considerable time in said dirt. It doesn't look super grimy, but it sure doesn't look pristine white anymore, either. Furthermore, the soil around here has a high clay content, so the dry stuff tends to have a texture similar to talcum powder! You may cerainly have something here; keep the theories coming!

Treeman, thanks for your input. I feel very encouraged by your comment that you have never known a Blake's to allow a freefall. It's true that it'll take a while to trust the knot again, and I will use some safety knots for that while, but just from the feedback I've received here I'll feel more confident on my next climbs. Please tell me, though, what's a B-53 knot? Is it a 5/3 Blake's?

I thank you all, and my inner kid thanks you, too!

Brad