Is he at that stage where shoes magically disappear?
I always have to laugh when I hear a parent exclaim "Where are your shoes?!!".
I remember those days.
Our son is 21 months and when we went last month I found his Crocs to be the easiest. Yes, he can get them off the easiest but we can put them on the easiest too. One day I tried his Converse because I thought they'd stay on but he can get those off too and they were a PAIN to get back on. His Crocs were even easier than his sandals because his sandals had velcro. Luckily, we never lost any. We always found it before it was gone, usually by running over it with the stroller .