Something I found rather effective was building to 10 minutes of total work instead of just a 10 minute block of time (when I had a free block to do so).
I would do wall runs as long as possible, then after the first time coming down, I would do sets of 30 seconds until 10 minutes under tension had lapsed. I saw results very, very quickly. I started with only being able to be in the wall run for 1.5 minutes and in 2 weeks time would reach 5 minutes before having to come down. I love and hate wall runs. Love the results, hate "feeling" so heavy near the end.