This is why King's Guard stand up when a horse wees at Horse Guards in London 

You lean forward and stand in your stirrups to relieve pressure off the horse's back to make it more comfortable. The kidneys are positioned anatomically high with the bladder under and behind them, almost directly under saddle, and a rider should always pay due respect. ❤ 🇬🇧

That guard is a gem. No nonsense with a bellowing voice.. Excellent Trooper

A crowded, noisy place, long time standing there. Those horses must be , to say it lightly, tired, bored, annoyed.