I have been reading the post by KNollslinger and the like on the difficulty of recovering long range projectiles.  I was visiting my mom in OH over thanksgiving and went up to Dundee MI to Cabellas.  I found these little flashlights that were on clearance for like 6 dollars.  they are LED and have 5 different modes two of which are blinking.  They are about the same size as a sling glande and I was thinking if you could add enought weight to it and it would survive the flight and impact you could recover it fairly effectively, especially at dusk.  The flasklights are really cool and I only got two of them so I cant throw mine but it may be the step off for some good trackable sling ammo.  Build a small solid state light beacon and make it heavy.  You could even make it so it would turn on on impact.  Or better yet a very small radio transmitter.  Wow sorry my mind just ran away on me.  I might have to build a little LED beacon though.

Joe

I think perhaps just throw at a house as you approach it till you hit it.  THen mark the spot.  RUn like crazy and comeback someother time to measure?

No.. that is bad.

Do same with a billboard?