Store it in an airtight glass up to a few weeks
If you don't possess a food processor you can also use a hand-held blender or even a mortar and pestle. If you use a mortar make sure to pestle the ingredients bit by bit.
You can prevent pesto from going off by covering it with more olive oil. The oil seals the pesto and keeps it fresh
Don't make this pesto or don't try this pesto right before you have to see clients. After all it's made of garlic ;-)