Question: Why does my young gelding sniff hay and then pee on it?

Answer: Your gelding is performing natural elimination marking behavior. While most commonly seen in stallions, geldings and some mares will exhibit a series of behaviors including sniffing and otherwise examining something, such as a pile of hay, a particular patch of grass, a pile of manure, or a patch where another horse urinated, assume a position over top the area of interest, and then urinate or defecate over top. Stallions are notorious for creating “stud piles” along fencelines or other areas demarcating their “territory”. 

Question: I read your article about “Introducing horses”.  I would just like to ask your advice.  I have a mare (12) and a gelding (24) who have been together for a year and a half now.  The gelding is used for lessons but being as old as he is, I needed to buy another school pony to take the workload off him.  I had leased another gelding a while ago but my gelding just would not accept the new
gelding.  He constantly went for the new horse.  I introduced them all slowly and in their own paddocks but when it came to putting them together, it was an absolute mess.  I had to give the new gelding back.  I have now bought a young mare for the school and already he is going for her over the fence!!  Please could you give me some advice.  I really don’t know what else to try.  I’m desperate to get them together as my 12 year old mare is leaving soon and I don’t want any horses to have to stand in separate paddocks.  I only have limited grazing so I need them to be in one paddock while the other two paddocks rest.
Thank you so much for your time.