How do billionaires protect themselves against assassination? What do they feel about security everywhere ?
Billionaire should understand the importance of their lives and protect it in every possible manner.

They have so much materialistic blessings, which is more than most of us have. This disparity causes jealousy, and hence Billionaires become a target of poors.
To snatch the wealth from them, poors plot deceiving acts and conspiracy against these Billionaires.
Only smart Billionaire will be able to perceive these traps, and save themselves from it.

These traps can be like some unexpected moments in the lives of Billionaires, where they may get physically assaulted by the poors.

Or their lives may be vulnerable to the poison in the drink or bomb in the cake.

Hence Sometimes, Billionaires may have to take matter in their own hand.

For this, they have to be prepared always, which can prove to be a overwhelming and burnout for them.

Instead, these Billionaires should build a Agile security team for themselves, whose sole purpose should be to protect the lives of these Billionaires.

This security forces should be spread sparsely all across their premises.

The Billionaire should also make sure that their residence and work buildings are like citadel, with only one main entry.

And the security guards roaming around should be well-armed in the most secretive way.

When you are a Billionaire and some Guest comes to meet you, she or he should go through several buffer areas where security guards are roaming in a more social manner to avoid suspicion.
This will also help reducing the uneasiness a Guest may feel while being surrounded by armed guard.

After the Guest has gone through all these buffer areas, she or he should also face the ultimate interface door which is the final frontier between you and the outside world.
You should place your most trusted guards on this door to prevent any mercenary casanova from sliding into your room.

Needless to mention that their shall be further more Guards inside the room you reside.
The trust level needed for these shall be of highest level, because they will be your bodyguard, and shall be willing to take the bullet shot toward you.

Once you setup an intense security Guard system, which will be around you all day long. Then, there are good chances that as a Billionaire, you may get bored by seeing their faces again and again.
Hence, it is of paramount importance, to select only those guards which you like to be around with and you should dress them as per your fantasy.

These bodyguards should be those with whom you can share your most intimate moments.

Like, while taking a soap bath and shower.

Or while drinking and eating.

Or while meeting some client and doing your business.

Or when you are chilling out in your penthouse and playing video game.

These Guards should be with you night and day.
Also, if you like to travel via Car, which runs on roads and goes through many public places.

You should make sure that it is bulletproof and has thick armour to save your life even from a Rocket Propelled Grenade ( RPG ) attack.

When you are outdoors and not protected by wall or armour, you should keep your mobile squad of Guards with you all the time.
Like, when you are at beach or going on an enemy destroying mission.

Or while riding a water scooter or a powerboat.

Or while travelling by air using Helicopter or Private Jet.

Or while riding a bicycle or an elephant.

No matter where you are, your bodyguards shall be trained to attack enemy on the first sight of threat.

This is only possible if guards you choose, are dedicated and move with you like your shadow or wives.

Once, these bodyguards are chosen on the basis of their loveliness to you, they should get both weapons and physical training.

The weapon training should be organised regularly to keep their shooting skills sharp.

Physical training shall be even more regular than Weapons training.

The guards should be routinely tested for their flexibility to adjust to your special requirements, as well as to react efficiently to the unexpected challenges.

You should also be a participant in most of the above activities as well as chill out with your bodyguards, so that they feel emotionally attached with you.
This will not only increase their loyalty, but their performance as well.

However, being a Billionaire, you shall always be cynical. Apart from taking care of their health, You should make sure that all your guards go through routine loyalty and sanity test.

Housekeeping part of this security guard system require you to be ready for the situation where you, as a Billionire, may have to carry your bodyguard on your shoulders in the cases of contigencies.
This is an additional reason for a Billionaire to take part in physical trainings with his or her bodyguards, to keep him/herself in a good shape.

The loyalty and trust of bodyguards needs to be evaluated sporadically with some demo missions.
It should be made sure that these guards are ready to jump with you anywhere, anytime.

After the whole Security system is in place, routine drills shall be called out to monitor and improve the response of your team.
Any defection or weak links, needs to be eliminated, before they sink the whole ship.

The biggest challenge for effective working of this Security system is the Talent Management, which involves Hiring, Firing and Attrition.
Thus, regular Contest should be held in your swimming pool area to recruit fresh talent on the basis of their potentials.

Serious Billionaires, like Gaddafi, maintained their own small bodyguard camaraderie.

With the methods we have discussed above, we can build a much better and bigger security system.
I hope my Billionaire friends will find this answer enlightening.