  The theory of elasticity and pinning of domain walls in helical magnets is
presented. Domain walls perpendicular to the helical axis show non-local
elasticity and are marginally pinned by local disorder. Weak anisotropy
combined with magnetic dilution leads however to a non-local bulk pinning
effect. Domain walls with other orientations include generically vortex arrays,
similar to type-II superconductors. Their pinning force is calculated as a
function of wall orientation, pitch angle and impurity concentration. It is
shown that metastable domains can vary between needle and pancake like shape.
