Gophers - killing and compassion

There are 2 small areas I am working with this year - and they each got some rodent living in the ground - some rodent that EATS ROOTS...and in the process kills the plant. Earlier this year - I could hear it sometimes in the early evening, as well as see the plant move - in this case beautiful healthy and healthy soil giving clover - now 98 % gone.
We have a rat terrier, Storm the Wonderdog, who was supposed to catch some, and he did actually, elsewhere. We do have a cat wondering about too. I considered some poisonous plant seed briefly, but then decided against that.

One of the little patches has some transplanted baby strawberry plants on it and the other day I also put some beans in the ground. So I decided to water the area really well. And it got soaked - in addition, I took the hose and watered any area that might have been missed - and then THERE IT WAS - grey wet rodent, best I can tell, a pocket gopher, coming out of the hole, getting air, trying not to drown ...slow moving and wet, it was under more splashing water - where was
Storm???????????????

I could have killed it - there is was, poor, grey, wet, cute creature - just doing what he was born to do. Without doubt a sentient being ... and there is no way I could have killed it.

Why? For one - how can I possibly kill this little furry creature? And secondly, I don't have the right to. I don't have a good reason to. Nothing I can think of would justify killing it.
If I really depended on those beans for my life - we'd have to talk - but I don't.
If I really depended on those beans to live, I might have to catch and fry it for food, but I don't.
If it was injured and suffering - it did not look like it.
If it carried some dreadful disease - I don't think so.
If the garden was totally overrun by them - but it isn't.

What constitutes real necessity to kill?

And it was cute too - and of course it got away.

...and of course, it finished off another bean plant the next day.

I figured I'll keep the area so wet that he'll move to another spot more to his liking. Not sure yet if it's working.