I once had a garden where lily of the valley had become a weed. But, then, I suppose weeding is just part of gardening, the process of choosing which plants one chooses to allow in one's garden.
I have read that it is best to plant them where their roots are confined and they can't spread too much and that they do fine in pots. i have no personal experience of this. They like moist soil and don't mind quite deep shade, but also survive in sun.
Wait til they have died down completely ( late summer/autumn) and then you shouldn't have a problem
Oops......conflicting advice here
My L of the V are just coming into flower now so for me waiting til later would be best. Pick out your spot and try your best not to succomb to sticking something else in there in the meantime.