jpm1 speaks rightly... even 7 strands of 4 point barb will NOT stop a determined **** sapiens, neither will any combination of electric or barb wires. At a correctional facility, it takes a man dishing out lead poisioning to enforce the fence, on occasions.
So, you are seeking a combination of realistically priced deterrent forces to reduce the number of people who "want to" enter your property. There will always be some who are undeterred, I fear, and will require your most aggressive legal attack.
I am guessing that the deterrent percentages are as follows:
0-95%>prior knowledge they are unwelcome... thus drive elsewhere ..increases over time depending on success of following deterrents.
80%>observing sign that property is posted (your number)
3%>observing placement of boundary fence making it very clear that entire property is posted with no very easy way in.
3%>consider too difficult for all in party to go over 1 strand of barb
3%>consider too difficult to go under 1 strand of barb without getting on ground.
3%>consider too difficult to roll under barb wire..increases with success of cactus plantings
3%>discover that wire is electric and don't want any part of it anymore.
= 95% that leave without entry to your property.
5% invent a way past the fence (I think this will be true, regardless of what kind of fence you have) via destroying it, shorting it out, climbing over, under, etc....
4.5% of these are convinced by a combination of non specific gunfire and/or factual confrontation to leave the property.
oh, yes, just realized...TAKE A VIDEO CAMERA WITH YOU AND RECORD THE TRESPASSER AND YOU ASKING THEM TO LEAVE and their reaction and leaving or refusing to do so...date and time stamp the video as it is recorded. Now, for repeat offenders, you have very specific details of who, when, where it happened and what they did about it....do this with your shotgun on a sling over your shoulder and KEEP YOUR DISTANCE from the trespasser.... in the end, you need to be able to defend yourself from knives, multiple people, etc..... Unclear what the law in Spain says about self defense, but in Texas there is the Castle Doctrine which still applies.
leaving .5% that require legal dealings .... hopefully, less than that.
that's my $.02 worth
If you start with one barb wire and are dissatisfied, you can place a 2nd barb line about 6 inches off the ground...making it hard to go under while still making it hard to wrap the two wires together and shorting out the entire fence...