If you do not have enough pasture, and it is eaten bare, you can bring forage in, or bring the sheep to the feed.
They can be tethered: fastend with a rope to a ring around a picket in the ground so they can graze in a circle. You can also attach the rope to a line between two pins, which gives more space. Regularly check whether the rope is not binding or sticking around legs, shrubs,… Around the neck you obviously do not hang a snare, but preferably a loose belt, provided this is not sliding over the head. Use to the neck (band) and the attachment loop eyes that can rotate 360⁰ so chain or rope can not twist and turn themselves into knots and loops. You can replace the rope (partly) by a pole who must be longer than the rope, so that rope, stake and pen will not tangle. You hang one animal on one pen. Several animals you tether far apart, so they do not entangle and strangle each other.

geittuierenA tether (wire or cable) is used to stabilize tall, narrow structures (towers, wind turbines)
by anchoring them with an angled rope to the ground. Also used for balloons, astronauts…

Known from Westerns, the hobble or fetter, a kind of cuff that is laid around the feet of a horse or ox to obstruct it in his movements. If there is no fence or tree nearby, connect two legs (front, rear, crossed or sideway) with a leather belt, chain or wooden stick (or combinations thereof) attached to each other so that the animal can graze, but not walk too far away. It is used for short periods (e.g. lunch break), and preferably with soft material (belts, upholstery) to avoid that the animal gets hurt.

A variant, also used at camels, consists in bending one leg, and to bind upper and lower leg together. Or fixing one leg high (e.g. with a strap at the neck) so to make the foot cannot touch the ground.
Shackles and fetters were also used for prisoners.