Buddhist temple in Mount Koya

My hushand and I are going to Japan next week and would like to stay overnight at a Buddhist Temple in Mount Koya. Does anyone know if we have to make a reservation in advance or can we just arrive at the buddhist temple on that day for our stay?

we booked ahead, through this site: http://www.japaneseguesthouses.com/index.htm

they were very helpful.

I believe some people have turned up on the day and found places, but personally I like knowing where I am staying at least one night in advance. (although they do require more warning than that through the website)

You probably would be able to find a place on the day you arrive in Koyasan as there are many shukubo. There is a tourist info center at the entrance to Okunoin cemetery. Ask the worker there and he will call around. You also pay him whatever the rate is. Just be aware that some of them have different meal plans that you choose from regular to deluxe. Don't know if they would be able to explain that to you unless they speak english. Good luck.