I've been working on a beacon which I can deploy at various locations away from my home to do path tests with.
It uses IR so not to catch the attention of any passers by !!

First tests look encouraging as I can detect the beacon over a 10km path which is obstructed by only trees on the horizon.
The Rx is a 25cm square fresnel lens and 4x BPW34 Photdiode Rx at the focal point - info here: http://m0dts.co.uk/index.php?tag=OpticalDx&item=199

Signals vary a lot and light rain or mist seems to help.
Cloudless clear days do tend to give worse results.

The Beacon consists of:
Arduino Nano
NEO-6M GPS Module + antenna
IR LED - I'm using an SFH4715 on a 'star' heatsink
A handful of easy to get components.
Some code!

Here's the schematic
IR_Beacon.pdf

Here's the Arduino Project:
LEDBeaconGPS_v2.zip

Here's a image of the beacon in first use, I plan to make a pcb next to make it a little less of a 'bodge'.

mk1 top

mk1 bottom

A plot of the signal one evening while there was light rain on the path:

Signal Plot in 1mHz bandwidth