I was trying to design a set of magical shackles based upon the Perdo Vim effects which limit casting totals, but then a new thought occurred to me. A sufficiently powerful Mentem spell can change the targets memories completely, or limit use of a power or ability.
A spell which temporarily rewrites the targets memories so that they forget they’ve learned magic, or perhaps prohibits access to how to use those skills will be just effective. Unfortunately that level of memory alteration is also a effect base 25 and means a spell utilizing that effect will be exceedingly high.
As an alternative the spell Blessing of Childlike Bliss does exactly this (Ars Magica p.151), so is perfect. When placed in an enchanted device to neutralize a magus it might look like:
Shackles for the Non-compliant Magus
Perdo Mentem 50 Enchanted device.
The wearer of these shackles has their metal capacity reduced to that of a child, akin to the effect Blessing of the Childlike Bliss. They cannot cast spells, and will problem solve and reason like a child.
(Base 10, +1 Touch)(+14 levels for constant effect, +21 for +42 penetration)
These effects, like all the others I’ve pondered are part of a new spells compendium for Ars Magica.