It doesn't matter if he owns the land or not. If he owns the STALLION then he is responsible. The only way he might not
be responsible would be if he was at a boarding facility. If it was a boarding facility then they BOTH may share in the responsibility.
As for who keeps the baby. The mare owner keeps the foal or else has it destroyed in utero. It is their decision/choice. If the baby is not destroyed, then the owner assumes the responsibility of the mare and her health regarding subsequent foal. If mare owner decides to keep foal and for whatever reason mare dies (say in giving birth) the stallion owner is NOT responsible at that time.
We actually had a mare of ours (at a boarding facility) get impregnated by a very high $$ stallion. (BO stallion) We decided to keep the baby, and the stallion owner filed a breeding report so we got a nice baby out of it. (They probably did that so we wouldn't get mad(er))
I have known people who have had ignorant stallion owners that have had to threaten to shoot because stallion went nuts on their property (and kept comming back to wreak havoc) but never had to do it myself. I am currently a stallion owner but fortunately my guy is VERY much the gentleman. We actually have the opposite problem. The mares break INTO the stallion pen to get to HIM!!