Hi,
right, toroids have a LOWER leakage flux respect to
conventional transformers, but they still have.
I had problems with toroids and i solved them in two ways:
1) wrap the toroid with the same iron foil used to make the core,
a 5mm shield reduced (in my application) the LF interference
of at least 6dB.
2) orientate the transformer (moving it circularly around its
fixing bolt) to minimize the interference.
3) (not listed) if it is difficult to shield the interference "source"
(the transformer), you may try to shield the "receiver" (the
sensible area of your application).
In my opinion, since it is not a ferromagnetic material,
copper is not suited for magnetic field shielding.
Bye everybody.