Stationary Swimming

I bought a belt and some surgical tubing a little while ago.  I rigged it up to allow me to connect it to the lanelines or the wall.  This enables me to swim in place when I can't get a full lane to train in.  Lately I've been timing myself while I swim all out.  I began at only about 10 seconds.  I've worked my way up to 15 and then 20 seconds of ALL OUT swimming (100% effort).  Today I focused on kicking after my full 3,000 yard practice.  I strapped myself to the wall and did some moderate kicking to see how long I could last before losing ground and approaching the wall again.  I wore my short fins to work my legs more.  My first attempt was only about 35 seconds.  The second was 50 seconds and the last one was 58 seconds.  My goal is to combine these two sets to swim all out for 1 minute.  I feel that achieving this goal will give me better endurance for my 100 yard/meter races since I'm swimming as long or longer than I would have to swim WITH turns (turns allow certain muscles to rest while working others).  I've got quite a spread to cover between 20 seconds of 100% effort and 58 seconds at 50% effort.  I had a nice conversation with my former middle school coach while at the pool.  People are so nice.  She was coaching a 10 year old as the girls father watched from the bench.  My equipment bag was next to where the father was sitting so when I walked by I said hi and "I remember my father watching my swim classes", he chuckled and replied "oh yea?".  I followed with, "yup, and I'm glad he did".  The man smiled and I headed into the locker room.