Toggle-type device

A Toggle-type device is a releasable and retrievable advanced anchoring device. Using a Toggle is a ghosting technique as in normal use it leaves no artifacts behind. Toggle devices are often referred to as FiddleSticks after the widely-available version made by Imlay Canyon Gear. Using a Toggle is referred to as Fiddle Sticking or Fiddling.

How to use

Toggle-type devices are designed to work with two ropes: a rappel rope and a retrieval rope. The rappel rope is passed around a secure object such as a stout tree or smooth rock with enough extra length to rig a specific version of the Stone knot. A Toggle is substituted in place of the carabiner in the Stone knot. To pull the Toggle from the bottom of the rappel, a retrieval cord is tied to the Toggle and lowered to the bottom of the rappel. When the Toggle is pulled out of the Stone knot, the Stone knot collapses leaving the clean end of the rappel rope free to be pulled from around the anchor.

Using with one rope

Unlike most rigging systems, Toggle systems require two ends. If using only one rope, then both ends will be used in the rigging at the top of the rappel. This means only the middle of the rope will be dropped to the ground in preparation for rappel.

Advantages

Normal use of a Toggle leaves no artifacts behind.
Because of its low friction upon retrieval, a Toggle allows use of objects that are far back from the drop or quite large, that would not normally be considered for an anchor, or would require large quantities of webbing to rig.
The rope that must pass behind the anchor is a free end rather than a bight (unlike the CEM knot), which is less likely to catch on things during retrieval.
A Toggle does not require pulling the rope through a ring. Thus it can be used with a rappel rope that has knots in it. It can be used where pulling a rope through a ring would not be practical.
A Toggle tends to produce fewer rope grooves than pulling a rope through a ring.
On long rappels, a Toggle is used with a light weight pull line, rather than a heavier rope.

Disadvantages

Like all releasable anchors, Toggles present a higher risk of accidental release while on rappel.
If using just one rope, both ends must be accessible and this may mean taking the entire rope out of the bag (unlike the CEM knot). NOTE: It's much easier to use 2 ropes (or a rope and pull cord) with any toggle device.
Because the free end of the rappel rope must be at the top of the rappel, the bottom end of the rappel rope is usually not free to rotate to release twists. This results in putting twists into the rope, especially with eight-like rappel devices, making it more difficult to deploy rope cleanly at the next rappel.
Toggles cannot be used on "messy rappels", raps with intermediate rocks or logs (etc.) that can catch the toggle during retrieval.
Not all Stone Knot variations work. Only the upward overhand stone knot releases reliably.

Notes

The Stone Knot can be placed anywhere between the anchor and the start of the rappel. Thus the toggle can be located where it will work best - usually where it is in the air and clear of rocks or surfaces that might push against the toggle.
The weight of the retrieval cord should be managed carefully. For rappels up to 100 feet (30m) a normal lightweight canyoneering rope can be used. For rappels between 100 feet and 200 feet (30m - 60m) a 6mm pull cord works well. For rappels longer than 200 feet (60m) a super-light toggle pull cord such as an 1/8" woven dyneema cord works well.
Very soft ropes like the Sterling Lux can over-tighten on the toggle, and not be retrievable.