Create a reflection spell talisman to carry with you or hand on a wall or in a window at your home office or car. This takes three days to craft.
I use the plates from inside an old-style computer hard drive or a mirror. On the surface in the color of each element, write the Faux Latin word Reflectus. You can also add runes, script, or glyphs etched into the mirror/plate.
Pass this through the smoke of your favorite protection incense; take it outside and show it to the sun or the moon while explaining to the goddess why you need its protection;
now dip it in running water and ask the naiads and other river dwellers to bless the surfaces so that they will reflect all things even magick;
leave it in a bowl of polished stones overnight to reflect directly back on the caster or buried a bowl of sand to disperse the energy;
the next day affix the talisman to a chain, rope, or hemp DNA Weaved ( ); activate it by holding the plate or mirror in your bare hands and visualize a white light moving from your projective hand (the one you first learned to write with) to your receptive hand which caused the plate or mirror it seem as though it is being heated up by pure divine essence.
After this, hang it on a wall or in the car; around the neck, in a pocket, or around the wrist or ankle of the person to be protected.
A variation on this is Harry Dresden's Shield bracelet from Jim Butcher's fictional Dresden files novels; where the form is of small medieval-style shields on a leather cord that is worn around the wrist.
The Dresden Version seems to be more reactive than active so, I would use the above forms, but add a switch or a button (either a RW one or a runic representation) after the activation charge and visualize the switch to be like a dam that is holding back a massive amount of water/power. So when you set the switch off all of that water/power flows into the shields and provides protection.
Thankfully in our world, unlike Dresden's supernatural Chicago, we will rarely be involved in a situation where we must call a shield into being at a moment's notice, but having it sussed out will prove useful if the one in a million chance unless you are the pagan Ed and Lorraine Warren, that you do require such a thing.
Good Luck and Be Safe. In Servitio Somnii