How to hide scrying sensors

[MichaelCullen]

So the normal perception DC to spot a scrying sensor is 20+spell level. By the time scrying comes online, almost anyone can make this check.

In 3.5 it was very difficult to spot a scrying sensor, it requires a DC 20 INT check meaning you needed a 30 int to even have a 50% chance of spotting one.

I think the 3.5 version was too difficult to spot, but the pathfinder version is too easy.

Besides hieghtening scrying spells, what ways are there to make them more difficult to spot?

[avr]

There's ways to mess with perception, but they require you to be there. Which defeats the point of scrying. Otherwise you need to look at variant rules like words of power - the way you can combine effects there should make it possible to hide the scrying sensor more effectively.

[Kayerloth]

Don't forget any applicable Perception penalties including distance between the user and sensor.

Slightly non-RAW but the sensor could be considered motionless and increase the DC appropriately ... it could be argued the base 20 is for the fact the sensors are typically invisible but some of them are mobile (Arcane Eye, Prying Eyes, for example). Or decide that being invisible is not included and is one of the Perception penalties to further apply (including whether its a mobile or not).

Also consider that some of the difficulty may be related to dreaded 'game balance' to make the equally dreaded Scry and Fry behavior more difficult.