Footstocks are feared by all slaves, who have ever experienced them. They are extremely restrictive and not entirely without risk.
Footstocks are quite extreme devices. All the slave can do is stand and usually even the slightest movement will distress her ankles. She has to stand and has to stand STILL. Knowing you have to stand completely still makes it twice as hard to actually do that.
There is a risk. If she falls, she may sprain her ankles. While you can easily prevent that from actually happening be securing her to the ceiling with a rope, that will not take the fear away. Besides, since any movement will immediately hurt her ankles, that fear is re-enforced several times per minute!
If you plan to have a session with footstocks you MUST make sure her body is sufficiently secured so she cannot fall and her legs can never make a severe angle to the stocks themselves. The potential risk of broken ankles and legs is VERY serious and you may cause serious injury if you do not secure her. Especially any action that will create contact between the board and the front of the legs is extremely painful. That may very well spark counter reactions that are entirely unpredictable, hence securing is a must.
Even if you are a hard sadist, don’t think that securing her will take any of the cruelty out of the situation. It will not. In fact, it will signal that she, although safe, is probably going to be in this demanding and humiliating position for a long time, which – to her – will only make things worse. Her genital area is fully exposed and ready for either torment or sexual stimulation. both of which will trigger movement and as a result: pain.
And there is another thing to consider: it more than a little likely that the skin will be chafed. Lining the hole with leather will prevent most of this, but bruises are likely to be the result no matter how hard you try to prevent them and the ankles and legs will be sore for several days after, especially if it is going to be a long session.
The final thing bear in mind: standing for a longer period of time may invoke fainting. That is not what you want to see happen to a slave in footstocks, so observe your slave at all times. Secondly, standing with the legs apart may be very demanding for people with existing back and hip problems.