Female urinating near new bunny!

[DelawareRunner]

I posted a few weeks ago about the two sisters I adopted (eight months old and spayed back in December) and both of them have adjusted well to my home and seem to be very happy. I decided to foster a one-year-old spayed female from the same rescue and she is housed in the same room as the sisters, but they cannot see each other unless they are free roaming and I put a pen around the new bunny's cage so they cannot bother her. Well, one of the sisters has started urinating near the foster! I even put the foster outside of the room one day and she still urinated near where the foster's cage was. The foster is a sweet bunny and I don't want to have to take her back, but all my rabbits have to be housed in this room for awhile. I never had this issue before and the urine will start ruining my hardwood floors, not to mention I don't like stepping in it. Anyone have this issue before? Will this just keep going on? Pic of the foster below:

 

[JBun]

Normal territorial behavior. It will likely subside as they get used to the new rabbits presence. I would suggest putting down a waterproof barrier to protect your floor. You can also put extra litter boxes in the areas where your bun is peeing.