Savil makes a startled "oof" sound. "Wow! I felt that. It - you didn't destabilize the barrier, but you...tunnelled through it? Like you were cutting through it with a much stronger spell than mine." 

"Huh, okay, so -" A bit of plastic pipe, hollow in the middle?

That one neatly slices and divides Savil's barrier into the main part and the little circle inside the pipe! Which immediately destabilizes, since she's not expecting this, and throws out some random sparks and static in the process. 

Cam sticks his arm through the pipe.

- Savil reacts as fast as she can and tries to block the interior with a new mage-barrier, but it's not very well anchored yet and sort of crumples when he tries to shove through it. 

"I could've maybe stopped you doing that with more practice," she says. 

"Hm. Does it matter how strong the material is..." Soap foam?

This seems to work just as well at making a hole in the barrier as stronger substances! 

Once it's there, though, Savil has a much easier time just shoving it out of the way and reforming the missing bit. 

How about something elastic, appearing squeezed to a narrow line but bouncing out into a cylinder as soon as it exists?

That behaves a lot more like a spell exerting force against someone else's spell! Savil can push back against the force, and squish and pinch it back to the narrow line, but this requires putting significantly more energy into the spell. 

"Okay, so I don't straightforwardly beat the spell but I can make it put in a lot of work - there's no reason I couldn't do hundreds of those at once - and that'll probably do the trick?"

"Good! I expect so. Want me to test a few variants on you, just to check?" 

"Sure."

"All right, this is the simplest one." 

Savil closes her eyes, concentrates in preparation for about thirty seconds, and then casts the spell. It's very similar to the original mage-barrier, except for the fact that it snaps tight around Cam's body like cling wrap, making it impossible to move. 

And if he covers himself in little barbs of frost?

Savil can keep the spell together for a few seconds by throwing TONS of power into stabilizing the mesh-like net of it left around the barbs, but she doesn't bother with this for long. 

"...Mm-hmm. You can get out of that one just fine." 

"Cool." He surrounds himself with some hot dry air to get rid of the frost and resulting icemelt.

"Well, that's by far the easiest kind of restraining spell - so most likely what you'd encounter - and it's one that your talisman won't block since it's technically not attacking you. There are some paralysis-spell variants that might be harder to shake off but they won't get past the shields. Want me to try a couple of the more sophisticated restraint based trap-spells, see if the same trick works?" 

"Sure, if you're not worn out or anything."

"Not yet! And this kind is actually a lot more power-efficient, just takes training and control that most mages don't have. And setup time. I'll need ten minutes or so, since I don't have the trap-spell set already." 

"Okay!" He has a library to read while she's doing that.

Eventually Savil's eyes refocus. "Ready?" 

"Hit me."

She hits him! 

This one, pre-prepared and triggered, goes up even faster. Instead of a single solid sheet of force, it seems to be made of - a very very large number of threads or strings of magic, crisscrossing each other almost like netting or cloth, and all of them constantly moving to evade being snipped one at a time. 

"Wow this feels really weird!" How does it take to the frost trick?

Not nearly as straightforwardly as with the last one! The threads are moving and slippery and some of them get disrupted but the trailing ends are "sticky" in an almost static-electricity-like way, and just glom onto something else. He's damaging the net but, so far, not weakening it very much.