If you are not going to breed your dog have your male neutered. Your dog will not become fat, Nothing makes them fat except too much food and lack of exercise. The health benefits alone are worth it. You can look to avoid:
Testicular Tumors, the second most common malignancy in males. Growths can occur as young as 2 years with the average 10-11 years. Testicular Torsion, potentially life-threatening. Infection, trauma, wounds and frostbite can also give and stress to the intact male.
Benign prostatic hypertrophy, occurs in more than 60% of intact males over 5 years of age. Treatment is usually unrewarding.
Neutering can help calm an overactive dog, helps with the wanderlust, and indoor urination. Prevents prostate enlargement and infection. Checks aggression. Not to mention preventing the male from accidental future litters!
**facts from Successful Dog Breeding by Chris Walkowicz and Bonnie Wilcox, D.V.M**