If you believe in deities like Jesus from Christianity you would know that the deities are always with you, but if you feel you have to know they are there I would recommend a simple evocation chant with your deity of choices name in it will do the trick.
Well personally i never had to summon mines she just appeared randomly, though she is invisible she helps me with others in a not so literal sense.like I call mines Mi'lady the first name that came to me, as she is a succubus with renascence nostalgia.Point is you can make a contract with any being as long as their willing and you have a bond.For example i did this with a fairy and she accepted it in the process of bonding.
As mentioned above you can in thoery get almost any spirit to follow you aroud and help. But it should be noted that they wouldnt be able to physicaly help you move objects or people. For a spirit to do that they would need alot of power.
From other people, such as physical attack? No. I would never trust the safety of my life with a magick protection or guardian spirit.
Although its always nice to include spiritual protection along with good decisions and safety precautions. For instance some believe in carrying medalions of angels, deities, saints, etc for this purpose. A Saint Christopher medalion has been passed down to me in my family, always carried by men given to by a woman. I gave it to my husband to keep in his pocket. Christopher is believed to protect against accidents and every person that has ever held this medalion in my family (including my husband) have experienced accidence that could have ended in severe injury or death, yet miraculously left them unscaved or only mildly injured.
From spirits and negative energy/magick thrown or given off by people? Yes. Servitors or simply thoughtforms.
If you do go down that route I suggest destroying it every week and remaking it. Also maintain it every day.
The best servitors are those attached to a physical object, ideally a piece of paper kept in a safe place that can be torn up to disperse the energy of your thoughtform. What happens to servitors when not maintained and destroyed and rebuilt is that they eventually gain an intellect and personality of their own. Since they do not have souls like we do, their energy is suseptable to being tainted by surrounding energy. Negative energy can attach to us in our daily lives and they are no different. They can become overly protective (like a wild dog), aggressive, or even malicious. So be sure to keep a good system going and make it a daily routine to sense it, and make it a weekly routine to fully destroy and rebuild it. If you do that, you should fine.