I got caught.....

Tell her the fire you'd drunkenly lit was getting out of control.

On a more serious note, as men get older they often find it more difficult to control their bladder movements. This does not only apply to incontinence, but also the converse - they can find it difficult to urinate when they are supposed to. It could be the case that when you stand in front of the toilet, you feel under pressure, as it's quite clear what the task you need to perform is.
However, you might subconsciously be avoiding this by standing in front of, for example, the fireplace - tricking your mind into a false sense of security so it does not feel the need to inhibit you - and then whipping your mickey out and letting rip. By the time the brain realises what is happening, it is too late to do anything much about it.