A few things you could do to ease your mind is to do a blood panel before surgery is done. This will tell you if your baby is healthy enough to undergo surgery. This second thing is my personal feelings about neutering: don't do it too young. I prefer 12+ months to allow the pup's body to fully develop (growth plates close). A pup can be trained not to mark. I trained mine not to mark, and have had success discouraging temporary fosters from also marking in my house. (I say discourage vs trained because they don't spend enough time in my house for me to be confident they are officially, fully trained)
__________________ Littlest JakJak 
We miss you Kaji 
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