Wash the olives, basil, and the arugula. Put them in a electrical blender and mix it all together to a paste.
Press the garlic with a garlic press, and add it to the pesto.
Pour the olive oil, salt and pepper in the mixture and mix it well with the electrical mixer.
The pesto should not be to liquid or too compact. If it is to compact you can add some more olive oil, and if it is too liquid you can add some more olives.
Put the pesto in the fridge for approx one or two hours before serving.