You've got to burn up some shoe leather and scout for them. I like to do this in March, because the foilage hasn't started getting thick yet, the sign from the past season is still somewhat fresh, and if you spook any deer they have a whole 7 months to forget about it.
Hidden funnels are just that...hidden, or at least hidden from where deer feel they can be observed easily. Look for slight terrain depressions in a field that can't be seen from a road or a farm building. Also where a gully or finger of woods or brushy draw extends out into a field, thus making the distance from it's tip to the woods on the other side the shortest distance across that field.
Did you ever look out across an area that looked to be pretty well flat, only to discover when you walked it that it was anything but? The depressions that you encounter here are likely "hidden" funnels.
I have found many funnels when I was blood tracking deer for myself, or others. You can learn a LOT about where and how deer move in your area by doing this. It also helps me to "think like a deer" when I look at an area, and I say to myself:
"Now where would I go to cross this field/woods/prairie if I wanted to hide from a pursuer?" The majority of the time when I do this, I find that the way I choose has deer sign in it, and for the same reasons.
Also consider the prevailing winds when you are doing this, as the deer certainly will when they use it. I use colored smoke bombs in my off-season scouting to educate myself as to what the wind currents to in specific places. It can be VERY surprising!
Like I said, you need to do some walking to find these, and preferably NOT during deer season. Aerial photos or topo maps of your area can also be a very helpful tool when you do this. It's work, but work that I don't mind doing in the least!
Or you can be like Jackie Bushman, and have someone else do all the work for you, so that you can just show up, wait a bit, and then pull the trigger! [:D]
Offer No Apologies.....
NRA Endowment Life Member