Here are few variations of the knee internal and external rotations with mini band.

Exercise 1 – Single knee internal and external rotation (foot on the floor)
Goalkeeper should stand in anterior 45 lunge, knee of the leg in front is slightly bent, body wight is on the front leg. In this position golkeeper is performing SLOW, CONTROLLED and SMOOTH external and internal knee rotation, while keeping the foot completely on the ground all the time. Focus should be on smooth movement of the knee.
Maintaining tall lengthened spine.
Do not rotate the torso or pelvis. All movement is made with the knee.

Exercise 2 – Single knee internal and external rotation (foot on balance pillow)
The same as in exercise 1, only now the foot is on balance pillow instead on the floor.

Exercise 3 – Double knee internal and external rotation (feet on the floor)
Goalkeeper should stand in little bit wider and lower stance. In this position goalkeeper is performing SLOW, CONTROLLED and SMOOTH external and internal double knee rotation, while keeping both feet completely on the ground all the time. Focus should be on smooth movement of both knees. Internal rotation is easier, so the focus should be on rotating knees equally much also externally. Maintaining tall lengthened spine.
Do not rotate the torso or pelvis. All movement is made with the knees.

Exercise 4 – Double knee internal and external rotation (alternate feet on the floor and on balance pillow)
The same exercise and focus as in previous example, only now feet are alternating once on the floor, once on balance pillow.