"As will melting it."

"That's an even better deterrent, yes."

"I found it so. But if you have no business of your own, I will be taking my leave."

"A protocol or signal for quickly contacting you wouldn't go amiss. Usually we use chakra flares and sensors to interpret them, but there's also seals that can be linked together for quicker communications, or technological solutions."

"A seal perhaps would be the easiest solution. My lair was not designed for human habitation."

"I'll send you with one. The most reliable ones just do alert flares - those can be used for a dot-code communication. More usable ones can relay more complex messages, but sometimes fail."

"I don't know your dot-code."

"Our best bet is likely a simple seal for an emergency flare, then, and a more complex one for communication. I can show you how to activate them - people who can manipulate chakra at all usually get the trick quickly."

"Please do."

He'll beckon her inside so he can fetch his supplies, then draw out the paired seals. He's not really explaining what he's doing, that requires talking, but he's not stopping her from looking, and he'll answer questions, albeit with as few words as possible. He then walks her through molding chakra and putting it into the seal.

She manages it.

...Distinctively different than mana, this chakra.

The flare seals light up for as long as she's channeling chakra through hers - Sasuke explains that it also gives a small burst of chakra, which is unique to the seal and either he or one of his warden sensors will pick up on it. 

The communication seal transmits sound, a bit wonkily, and cuts out if she shifts too much or her chakra isn't even, but it functions well enough.

It's likely to serve the purpose. It will do.

He nods, asks her if there's anything else, then forces out standard parting pleasantries.

(Why did he think leading a village wouldn't require far too much interacting with people.)

She takes the seals, and they get folded up with her clothes as she transforms to fly home.

When she gets back, she secures the seals in the main room. Then, she starts experimenting with shaping chakra.

It's not straightforward - the chakra wants to flow in its normal patterns, and is resistant to change, and misbehaves in different ways according to her emotions. But it's fairly easy to push small things away from her skin (even entirely on accident) - then to make them stick - then to balance them a small amount away, then farther. Elemental shaping is harder, both to manage and to control. 

She has lots of time to practice. Assuming nothing else bothers her.

Sasuke, meanwhile, is having a rather stressful time. Konoha seems to have moved against Ame - and given the information he's been getting in trickles and bits, that seems like a very, very bad move.

His few remaining Konoha spies catch wind of Jiraiya's death at the hands of Ame's - and the Akatsuki's - leader.

(He also doesn't know what to do with Itachi, his feelings about her have been all over the place (thinking he'd killed her was horrible beyond measure and he still can't believe he got the Mangekyou out of that), and if he can convert her, she'll be tremendously useful, but he doesn't trust her and she has no reason to trust him, and it's hypocritical of him telling his people to work alongside their enemies while he refuses to make a move one way or the other on his...)

But then he catches wind of the Akatsuki moving.

He's not sure he can leave his village undefended. He's not sure the Akatsuki won't take this opportunity to secure Isobu.

He sends an emergency missive - with Isobu on its heels - to the monastery, he knows the head monk there is powerful, and she accepts which is one problem off his mind - 

He arranges for his usual guard to take over Sound, she really does watch him do paperwork enough - 

And his second fastest hawk wings at full speed into Ellisaria's territory a few weeks after they last spoke, while his fastest carries an emergency missive to Konoha, him and a strike team as close behind as they can.

The hawk finds her at home, as is typical. Her lair has slowly been growing more refined as she spends time there.

She's in human form. She finds chakra easier to manage like this, similar to the more delicate spells.

"Emergency!" the hawk screeches. "The Akatsuki are attacking another nation's hidden village in force."

"And the boy requests my aid? Very well."

"Which way?"

He has a map, and can point the direction and give landmarks, both for Konoha and for the last known location and heading of the relevant hostiles.

"You might want to try meeting up with Sasuke-sama," he says. "We were tracking the Akatsuki's approach but they have rapid movement capabilities, it might change very quickly."

"I expect that will not be difficult. We are going the same way."

And she takes off, winging swiftly across the land.

His hawk veers to meet her when Karin senses her approach. "I suspect you're faster than us!" he shouts. "Are you willing to take Karin with you?"