Well, when Tor started making amulets from simple stones with glowing symbols on them, it came as a huge surprise for people as that requires two independent fields (one for the actual function of the amulet, and one for the glow).
By now, this should be pretty standard for most of the more accomplished builders.
I'm surprised that nobody has taken the next step by now.
Compressed earth currently seems to be the "top of the line" material for amulets. But the "maker" type devices are able to basically create any form of matter, with every single atom placed exactly where it's supposed to go.
With that tool available, it should be possible, using the the scientific method, to find some synthetic material with the best possible balance between ease of applying a field and longevity of the field.
I would assume that external forces (temperature differences, chemical reactions, EM radiation) affecting the amulet material are a major contribution to the field decay over time.
Also, for ease of physical handling, amulets are currently probably a lot larger than they would need to be when only considering the requirement of holding a stable field over a long time.
e.g. Tiera's implanted amulets (which everyone seems to have forgotten about after the ancients moved to the moon) are much smaller.
So, instead of creating large amulets from compressed earth with an always-on secondary light emitting field, create amulets from much smaller (say, rice grain sized) pieces of some optimized synthetic material, with an always-on (or, initialize once, then always-on) secondary field based a combination of the latest shield and clothing fields.
That way it's easy to have a larger number of the rice grain sized kernels in just a small box when initially applying the field (so no more running out of space just because you need a few million shields for all the people living on Mars in the future).
Once the field is applied, you pick up one of the kernels, hit it with an "initialize" intent, and it forms an inner shield around the kernel, which is as indestructible as possible, protecting the kernel from external forces, along with an variable outer shell that can take the form of an amulet (with necklace), ring, brooch, armlet, or whatever other shape is desired (programmable in the same way as the main clothing amulets).
This should be well within the abilities of the current top builders.