I've had three standard poodles and I've always done my own grooming. (It's so hard to get that run-over-with-a-lawn-mower look when you rely on a professional groomer.) Anyway, what everyone has said is true easier to get them used to toenail trimming young, much easier on a table.
That said, I've also had a couple of non-poodle rescue dogs, both large, that came to me when they were 7.5 and 8 years old, respectively. I'm nearly 100% certain neither had ever had their nails trimmed, much less been on a grooming table. As they got older and were less active, nail trimming was a must. (Both had dewclaws, too, which had gotten long by the time they came to me.)
As you noted, you don't want to get into a battle with an old dog; too great a risk of injury. Getting either one of my old ladies on the grooming table was out of the question, too. Too big and too frightened at the prospect.
I trimmed their nails with them lying on their sides and me kneeling next to their back and leaning across their bodies. (A killer for my middle-aged knees and back.)
A few tips:
1) Never "surprise" them with the nail trimmers. Tell them that it's time for nails.
2) Get them used to lying on their sides while you hold their feet first, before you introduce the trimmers. Reward them for each handled paw if they are calm with a GOOD treat. Nothing that says "dog" on the package. Use hot dogs, lunch meat, cheese, beef jerky for people, pieces of meat, etc.
3) A common mistake of people who don't groom dogs often is to soothe them at the wrong time. They say "Relax, That's a good boy, etc." while the dog is struggling. Don't be that person. To the dog, it can sound like praise for struggling. Instead, either say "No, calm down" in a calm but non-threatenting voice or say nothing at all while they struggle. The instant they relax say "Good boy, that's a boy!" and give them one of the super-high-quality treats.
4) After you've gotten them looking forward to lying on their side with you lying over them holding their feet, introduce the nail trimmer. At first, they get a big treat for every single nail. You may want to do only one foot at a time to start. (Or even one nail!)
5) Most dogs are a little calmer with a Dremel than clippers. Use the drum sander attachment and the #60 grit. The #120 is too fine. If the nail is getting hot but isn't getting ground away, you are using too fine a grit or you need to replace the sanding cylinder. Buy them in large quantities. It should take only a few seconds per nail. Best to use a battery operated Dremel, not the corded type. If you catch your hair or your dogs hair in the battery-operated one, the battery is not strong enough to wrap up hair as tightly as the electric.
6) I used to use a Dremel all the time, but got a little tired of it. The battery runs out of juice fast and you have to replace them every year or two. I went back to clippers. If you use clippers, use only sharp clippers. As soon as they start getting a little dull, toss them out and get a new pair. Otherwise, you'll be crushing the nails instead of making a clean cut.
7) Don't cut into the quick! Better to leave them a little long for next time than to give the poor dog a bad attitude by cutting into the quick.
. Much easier with 2 people; one to hold and feed small bits of Burger & the other one to trim. Still the burger keeps them distracted from their tootsies, but you better be done before the cheese burger is gone 
