Re: teaching my foal to lead, could someone give me tips?
I don't agree with the term 'controller' when it comes to halters. There is nothing which will control a horse unless it has learned to yield to halter pressure.
I use pressure type halters all the time, with all ages and types of horses, and I find them to be very effective for handling horses. However, it's not just a case of putting the halter on and expecting to be able to hold the horse if it tries to run off. Any attempt to hold a horse against its will amounts to force, and force is not a thing which helps horses learn.
If I were you, I'd use a pressure halter on the filly in the stable, and teach her how to yield to pressure. This is simple but very effective and, once achieved, will help your filly realise that she will not be hurt or made afraid.
The easiest way to start is to stand at the horse's head and slightly to the side, and use light halter pressure to bring her head toward you. She may resist, as the horse has an opposition reflex to pressure, but if you use a short pull to move the head only a few inches to start with, and an immediate release as her head moves toward you, the fily should quickly learn that as she allows her head to be turned the pressure wil cease.
After doing that a few times you can then apply light but constant pressure until she yields her head in your direction, and at each yield you can release the pressure, building understanding of the way pressure and release work. Then teach her how that works from the other side as well.
From there it is a simpe process to ask the filly to yield a bit more each time and, as she learns, to ask her turn a complete circle. By now this will probably be easily achieved by just moving away from her round the stable, having given her a quick 'signal' on the halter as to your intention to have her follow, and allowing her to do so. Teach her this from both sides.
Next, the filly has to learn how to step forward in response to pressure, and this is done using the same light pressure and immediate release when she responds. At this point you can begin to refine your responses by watching for a shift in her body weight in response to your cues, and at that point, if you release the pressure, the filly should follow through with the desired response.
Now you can teach her, by using the halter toward her chest to apply pressure over her face, and aiding her understanding with a hand on her chest, using the same principles of pressure and release, to step backwards.
Once your filly is reliably following round the stable, stepping forward and back, starting and stopping, with minimal cues on the halter, you can then start teaching her to respond to your body posture and demeanour so that she pays more attention, and you consequently need less halter pressure to cue her responses.
All the above should take about half an hour to teach, then she will be ready to be taken out in-hand. If, when you take her out, you handle her proactively, that is, by using subtle signals on the halter to keep her focussed on you, she should be disinclined to take off. Should she try, you will have the benefit of her understanding of how pressure and release to help you with control.
Remember, any piece of equipment is only as dangerous as the person using it. Used harshly, a pressure halter could be a cruel thing, but used to help a horse understand that it should stay close to the handler without being afraid...