I have had cats do this also. Get them checked by a vet for problems
first. If theres not anything wrong  then theres several things you can
do.
1) If its only in a couple spotts put his food and water there or a
bed. Somthing that he will not want to relieve himself near.
2) If its more than one or two spots put him in a small area with food,
water, bed, and litterbox this way he has nowhere else to go. let the
area get bigger like on room when you see thats hes used the litterbox
a couple times. After bout a week let him go about normally enless you
notice him reilieveing himself in other areas.
3) somtimes when cats are old they can,t make it to the litterbox so
you need to put one in every romm. We had to do this for our old cat
kitkat. She kept relieving herself in areas around the house. Well we
tried evreything else before we relized she couold hold it to get to
the litterbox. We found this out when she was running towards the
litterbox and she weted herself. Now that theres a litterbx in
everyroom then she doesn't relieve herself on the carpet anymore.

Hope this helps