OK, ilex..... understand, 4 barb wires already in place. I typically like to do least work for most effect.
Thus, suggest you leave 4 barb there, add signs.
Determine effect... while applying the random shotgun and factual confrontation approach. Cost of 4 wire fence has already been spent... add in line fence rachets if you discover that you need to tighten the barb wires frequently.
If you determine that more deterrent is needed, add 1 strand of hot wire inside existing fence... that is, on your side of the property line.
There are electric stand off insulators that are about 1 foot long that can be attached to T posts or wood posts and hold the wire away from the fence. Use the in line rachets for the hot wire and pull it tight...
The result will place a double obstacle for the adventurous... getting thru the fence AND around the electric wire. If you discover that it becomes a common practice to simply ground out the wire, then consider removing 1 or more wires in proximity to the electric wire.... however, you may at this point be reaching the limit of what can be achieved, regardless of fence configuration.
To answer your question specifically, yes, I was recommending a single strand of electric wire from which signs would hang, and a strand of barb a few inches off the ground, which would make rolling under the wire somewhat difficult and painful. Now that I understand that cost of 4 wires is already done, the only other thing I can recommend beyond signs is a single electric wire. Plus crazy acting and hunting activity and video of all trespassers to show the judge.
I don't recommend the brave bulls or cows approach... typically such animals are unspecific and unpredictable in their behavior... a person who knows how to read a bovine will be undeterred...even consider it a challenge. Often, cattle will move away from an unfamiliar person. If you are talking about fighting animals, when I was in Spain I saw some yearling fighting bulls in a pasture. when I stopped the car and got out to take a look...and they were 200 plus yards away, they became extremely wary and shortly ran away and over the hill. So, I anticipate that such animals would simply cause YOU problems and not do anything to address the trespassing issue. A dog could be a different story, depending on how dog is trained...
I think you are on the only path available... persevere and
Good luck!